AMUAtS 


EJECTS. 


HHHI 


LIBRARY 

UNIVERSITY  OF 
CALIF  OW 

DIEGO 


RY     | 

Y  OF 

..A  |  jj. 

Importing 


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/*. 


THE 


PREPARATION   AND   MOUNTING 


OF 


MICROSCOPIC    OBJECTS 


THE 


PREPARATION  AND  MOUNTING 


OP 


MICROSCOPIC  OBJECTS. 


THOMAS     DA.  VIES. 


Edition.— 6m(\\)  tfii 


EDITED  BY  JOHN  MATTHEWS,  M.D.,  F.H.M.S. 

Vice- Pro? .  Quekett  Microscopical  Club. 


NEW   YORK: 

WM.    WOOD    &    CO. 

G.    P.    PUTNAM'S     SONS. 

1874. 


PREFACE  TO  THE  SECOND  EDITION. 


reception  accorded  to  this  work  has  been  so 
favourable  as  to  induce  the  Publisher  to  issue 
a  second  edition,  in  which  such  new  matter  should 
be  embodied  as  the  progress  of  Microscopic  science 
might  require.  He  therefore  applied  to  the  Author, 
but  he  found  to  his  regret  that  the  state  of  Mr. 
Davies's  health  was  such  as  to  forbid  his  under- 
taking the  labour.  He  had,  however,  collected 
many  valuable  notes  and  memoranda,  which  he 
was  willing  to  place  at  the  disposal  of  any  gentle- 
man who  might  be  selected  to  edit  the  work.  The 
Publisher  then  consulted  the  present  Editor,  who, 
after  some  hesitation,  consented  not  only  to  use 
his  best  efforts  with  the  ample  materials  placed  at 


vi  PREFACE    TO    THE    SECOND   EDITION. 

his  disposal,  but  also  to  make  such  additions  as  his 
experience  might  suggest  in  extension  of  the  use- 
fulness of  the  book  to  a  new  class  of  readers, — the 
Medical  Student,  and  the  Junior  Medical  Practi- 
tioner. To  this  end,  besides  other  matter,  a  brief 
prefatory  chapter  has  been  added,  embracing  the 
elements  of  preliminary  histological  manipulation. 
While  claiming  the  indulgence  of  the  elders  of  his 
profession, — the  Editor  feels  that  the  best  and  truest 
apology  for  this  treatise,  its  raison  d'etre — in  fact, 
may  be  found  in  the  words  of  its  concluding  para- 
graph, to  which  the  reader  is  now  courteously 
referred. 

4,  MYLNE  STREET,  MYDDELTON  SQUAKE,  E.G. 
October,  1873. 


PREFACE  TO  THE  FIRST  EDITION. 


TN  bringing  this  Handbook  before  the  public,  the 
Author  believes  that  he  is  supplying  a  want  which 
has  been  long  felt.  Much  information  concerning 
the  "  Preparation  and  Mounting  of  Microscopic 
Objects  "  has  been  already  published ;  but  mostly 
as  supplementary  chapters  only,  in  books  written 
professedly  upon  the  Microscope.  From  this  it  is 
evident  that  it  was  necessary  to  consult  a  number 
of  works  in  order  to  obtain  anything  like  a  com- 
plete knowledge  of  the  subject.  These  pages, 
however,  will  be  found  to  comprise  most  of  the 
approved  methods  of  mounting,  together  with 
the  results  of  the  Author's  experience,  and  that 
of  many  of  his  friends,  in  every  department  of 


• 


microscopic  manipulation ;  and  as  it  is  intended 
to  assist  the  beginner  as  well  as  the  advanced 
student,  the  very  rudiments  of  the  art  have  not 
been  omitted. 

As  there  is  a  diversity  of  opinion  as  to  the  best 
mode  of  proceeding  in  certain  cases,  numerous 
quotations  have  been  made.  Wherever  this  has 
been  done,  the  Author  believes  that  he  has  acknow- 
ledged the  source  from  which  he  has  taken  the 
information ;  and  he  here  tenders  his  sincere 
thanks  to  those  friends  who  have  so  freely  allowed 
him  to  make  use  of  their  works.  Should,  however, 
any  one  find  his  own  process  in  these  pages 
unacknowledged,  the  Author  can  only  plead  over- 
sight, and  his  regret  that  such  should  have  been 
the  case. 

WARRIJJGTON 


- 


THE 

PREPARATION   AND  MOUNTING 

OF 

MICROSCOPIC    OBJECTS. 

CHAPTER     I. 

INTRODUCTION. 

THIS  work  having  been  written  chiefly  to  help  students, 
the  writer  does  not  venture  to  affirm  of  it  that  it  is  by  any 
means  complete  or  exhaustive.  The  art  of  microscopic 
manipulation  is  progressive,  and  it  is  scarcely  possible, 
therefore,  to  say  of  a  work  on  the  subject,  that  it  holds  all 
that  is  known  at  any  given  time.  It  is  an  art,  too,  which 
is  so  inextricably  mixed  up  with  the  highest  bra:iches  r.i 
scientific  inquiry,  that  new  modes  of  investigation  are  daily 
devised  by  the  acutest  intellects,  and  with  these  it  is  very 
difficult  for  a  writer  to  keep  pace. 

It  is  a  well-nigh  hopeless  task  to  attempt  to  teach  such 
modes  of  inquiry  by  precept,  yet  it  is  felt  that  some  short 
account  of  them  may  reasonably  be  expected  here.  Refer- 
ence is  now  made  more  particiilarly  to  the  practical  part  of 
human  and  comparative  histology.  As  this  is  not  a  treatise 
on  histology,  but  is  devoted  mainly  to  the  methods  of  pre- 
serving the  results  of  researches  in  that  science,  it  is  scarcely 
possible  to  indicate  to  the  student  how  he  shall  proceed  in 
any  given  case ;  yet  there  are  certain  tests,  reagents,  and 
staining  matters  employed,  with  the  uses  and  effects  of 

B 


2  PBEPARATION   AND   MOUNTING 

which  he  should  be  familiar,  so  as  to  be  able  to  speak  with 
some  degree  of  certainty  of  the  nature  of  the  tissues  demon- 
strated by  them. 

It  is  now,  therefore,  intended  to  give  the  reader  a  list  of 
these  aids,  arranging  them  according  to  the  effects  which  it 
is  desired  to  produce.  Strieker  observes,  "  that  it  is  to  be 
borne  in  mind  that  it  is  impossible  to  say  of  any  fluid  that 
it  constitutes  an  indifferent,  i.e.,  neutral,  medium  for  fresh 
tissues  of  all  kinds.  In  all  instances  we  must  be  prepared 
for  changes  taking  place."  He  gives,  however,  a  list  of 
fluids  to  which  structures  are  generally  most  indifferent,  i.e., 
in  which  least  alteration  may  be  detected  under  examina- 
tion while  fresh,  viz. : — 

1st.  Fluid  of  the  aqueous  humour. 

2nd.  The  serum  of  the  blood. 

3rd.  Amniotic  fluid,  very  fresh,  in  which  a  little  iodine 
Las  been  dissolved,  making  it  of  a  faint  yellow  tint. 

4th.  Very  dilute  solutions  of  neutral  salts,  such  as  phos- 
phate and  acetate  of  soda  and  potash,  &c. 

It  is  scarcely  within  the  power  of  any  one  observer  to 
have  largely  used  or  tested  the  whole  of  the  processes  here- 
inafter to  be  mentioned.  The  writer  therefore  freely  admits 
his  obligations  to  the  treatises  of  Drs.  Beale  and  Carpenter, 
Mr.  Qnekett  and  Mr.  Fownes,  as  well  as  to  those  of  Strieker, 
Frey,  Klein,  Schultze,  Kiihne,  Deiters,  Leber,  and  others, 
many  of  whose  processes  he  has  personally  verified,  and  of 
whose  manuals,  especially  those  of  Beale,  Strieker,  and  Frey, 
the  student  is  advised  to  possess  himself.  He  believes  also, 
from  his  own  early  experiences,  that  some  short  rationale 
of  the  intentions  of  the  processes  and  means  of  investigation 
used  by  well-known  workers  may  be  acceptable  to  the  stu- 
dent, in  repeating  their  experiments  before  embarking  in 
any  of  his  own. 

These  materials  and  methods  may  be  divided,  then,  and 
described  according  to  their  effects  somewhat  as  follows  ; 
and  it  is  in  the  judicious  selection  of  each  one  or  more  of 
them  that  the  tact  and  discretion  of  the  student  will  best 


OF   MICROSCOPIC   OBJECTS.  3 

be  shown.  He  should  bear  in  mind,  too,  that  the  same 
structure  may  well  be  submitted  to  various  modes  of  in- 
quiry, and  that  possibly  new  modes  may  occur  to  him  which, 
though  they  may  not  serve  to  prove  anything  directly,  may 
yet  become  negative  proofs. 

1st.  Such  tests  and  agents  as  render  transparent  or 
translucent  some  tissues  but  not  others  adjacent,  or  make 
some  more  conspicuous  than  others  without  colouring  them, 
or  at  least  but  faintly. 

2nd.  Staining  materials  or  fluids,  which  colour  either  all 
the  tissues  to  be  displayed,  or  some  particular  part  or  parts 
of  them,  thus  making  such  tissues  or  parts  more  conspicuous 
when  subsequently  examined  or  preserved  in  a  colourless 
medium. 

3rd.  Hardening  agents  or  solutions,  by  the  effect  of 
which  tissues  naturally  so  soft  as  to  break  down  or  be  other- 
wise unmanageable  under  manipulation,  are  made  firm 
enough  for  section,  or  for  such  examination  as  may  suffice  to 
to  discriminate  (or  "differentiate")  their  parts,  without 
either  disturbing  or  confusing  their  structural  relations. 

4th.  Softening  agents  of  animal  and  vegetable  tissues. 

5th.  Solvents  of  the  same. 

6th.  Solvents  of  calcareous  matter. 

7th.  Solvents  of  siliceous  matter. 

8th.  Solvents  of  oily  and  fatty  matters. 

9th.  Polarized  light,  by  the  agency  of  which  structures 
and  organs  may  often  be  optically  differentiated  as  a  pre- 
liminary to  other  modes  of  investigation. 

10th.  Electricity  and  heat. 

llth.  The  moist  chamber. 

In  dealing  with  structures  by  means  of  the  agents  com- 
prised under  the  first  division  of  our  list,  a  very  frequent 
and  necessary  preliminary  is  the  teasing  out  or  separation 
of  fibres  by  means  of  two  sharp  needles  set  in  convenient 
handles.  But  it  must  be  remembered  that  an  appearance 
of  structure,  where  it  does  not  really  exist,  may  easily  be 
thus  produced.  It  is  often  necessary,  also,  that  the  object 

B2 


4  PREPARATION   AND   MOUNTING 

shall  have  been  macerated  in  water,  or  some  other  agent, 
for  so  long  a  time  as  may  be  required  to  loosen  or  dissolve 
the  connective  tissue.  Tt  is  of  these  agents  that  we  shall 
presently  have  to  speak  in  detail,  greater  or  less  according 
to  their  relative  importance.  Boiling  or  steaming  may 
often  be  employed  with  advantage.  It  must  not  be  too 
hastily  concluded  that,  because  there  is  nothing  at  first 
visible,  there  is  therefore  nothing  to  be  seen.  There  are 
many  important  tissues  which  are  apparently  structureless, 
or  homogeneous,  which  yet  are  possessed  of  such  diverse 
elements  as  absolutely  to  require  some  process  by  which 
they  may  be  optically  or  visually  differentiated,  if  one  may 
use  such  a  phrase,  i.e.,  discriminated  from  the  neighbouring 
tissues  or  organs.  It  is  thus  that  their  proper  uses  and 
purposes  in  relation  to  the  whole  organism  may  be  correctly 
indicated  or  inferred,  their  histological  nature  decided,  and 
their  physiological  relations  and  connections  established  be- 
yond doubt. 

The  student  is  also  very  emphatically  cautioned  against 
the  use  of  objectives  of  very  wide  angle,  as  well  as  of 
deep  eye-pieces.  In  the  former  case,  the  relations  of 
structures  to  each  other  can  never  be  well  made  out,  since 
it  is  impossible  to  get  a  focus  of  any  depth  (i.e.,  of  all  the 
structures  involved),  in  one  view,  because  the  objects  in  one 
plane  only  can  be  clearly  seen,  the  rest,  either  above  or  below, 
being  more  or  less  out  of  focus,  and  therefore  hazy  and 
indistinct.  This  objection  applies  far  less  to  those  of  lesser 
angle,  which  are  therefore  the  best  for  histological  purposes. 
In  the  latter  case,  we  have  nearly  the  same  defect  to  con- 
tend with,  viz.,  that  surface  markings  only,  or  mostly,  can 
be  seen  clearly  (not  to  speak  of  the  loss  of  light).  The  use 
of  the  draw-tube  is  the  true  remedy  for  thia. 


OF   MICROSCOPIC   OBJECTS.  5 

1ST   DIVISION. 

Under  onr  first  head  may  be  ranged  the  following  : — 
Acetic  acid. 

Liquor  potassaa  and  sodse. 
Concentrated   sulphuric  and  hydrochloric  acids  (the  latter 

saturated  with  chlorine). 
Tannin. 

Lime  and  baryta  water. 
Oxalic  acid. 

Nitric  acid  with  chlorate  of  potash. 
Ammonia. 
Alcohol. 
Iodine. 
Glycerine  (?) 
Phosphoric  acid  (tribasic). 

Acetic  acid  more  or  less  dilute,  e.g.  one  part  to  five  of 
water,  after  a  sufficiently  prolonged  immersion,  renders 
transparent  the  following  tissues,  without  in  general  des- 
troying their  connective  tissue: — some  muscles  (of  the  frog 
(KoIIiker).)  cell-walls  generally  (not  the  nucleus),  epithelial 
structures,  white  fibrous  tissue.  Dr.  Beale  says  that  yellow 
fibrous  tissue  is  unaltered  by  it.  Many  kinds  of  formed 
material,  sections  of  preparations  which  have  been  hardened 
by  alcohol.  Dr.  Beale  also  says  that  it  dissolves  granular 
matter  composed  of  albuminous  material,  and  that  many 
tissues  are  quite  insoluble  in  it,  though  they  are  not  ren- 
dered opaque  by  it.  Acetic  acid  renders  some  tissues  trans- 
parent by  dissolving  out  the  phosphate  or  carbonate  of  lime, 
which  they  may  contain,  but  it  has  no  similar  solvent  power 
over  oxalate  of  lime.  Parts  which  are  unaffected  by  this 
acid  are  then  made  more  conspicuous. 

Liquor  potassae  and  liquor  sodas  act  in  much  the  same 
way,  according  to  the  degree  of  their  dilution,  but  on  different 
structures.  Albuminous  tissues,  epithelium,  &c.,  are  either 
dissolved  by  them  or  rendered  so  transparent  as  not  to 
obstruct  the  view  of  the  subjacent  structures. 


6  PREPARATION   AND   MOUNTING 

Concentrated  sulphuric  and  hydrochloric  acids,  used  cold, 
cause  epidermic  structures  to  swell  up,  so  that  their  cells 
may  be  easily  separated. 

Tannin,  dissolved  in  water  or  rectified  spirit  of  wine, 
hardens  gelatinous  and  albuminoid  tissues :  it  also  makes 
them  shrink.  Its  solution  in  water  has  been  used,  as  men- 
tioned in  another  part  of  this  treatise,  as  an  injection  pre- 
liminary to  one  of  coloured  gelatine,  to  prevent  extravasation 
through  the  walls  of  the  blood-vessels.  It  also  colours  the 
tissues  a  fawn-colour,  or  a  very  faiut  brown. 

Lime  water  and  baryta  water,  especially  the  latter,  will, 
according  to  Rollet,  dissolve  the  animal  cement  by  which  the 
fibres  of  connective  tissue  are  held  together.  After  a  few 
days'  soaking  such  tissue,  as  well  as  tendon,  may  easily  be 
teased  out  by  needles. 

Oxalic  acid,  in  a  cold  saturated  solution  (1  acid,  15 
water),  according  to  Schultze,  "  causes  connective  tissues  to 
swell  up  and  become  transparent,  while  those  formed  of  al- 
buminous substances  become  hardened  and  isolated..  Ex- 
tremely delicate  elements  of  the  body,  such  as  the  rods  of 
the  retina,  &c.,  are  thus  well  preserved." 

Strong  nitric  acid  mixed  with  chlorate  of  potash  destroys 
connective  tissue  in  a  short  time,  and  is  therefore  a  good 
medium  for  isolating  muscular  fibres  (Kuhne). 

Sulphuric  acid,  highly  diluted  (1  to  1,000  parts  of  water), 
used  warm,  gelatinizes  connective  tissue,  and  is  also  useful 
for  the  isolation  of  muscular  fibres. 

Strong  hydrochloric  acid  dissolves  the  intercellular  sub- 
stances of  organs  abounding  in  connective  tissue. 

Ammonia  acts  on  animal  matters  much  in  the  Bame  way 
as  potash  and  soda. 

Alcohol  coagulates  albuminous  tissues,  and  makes  them 
opaque.  It  corrugates  most  transparent  membranes,  and 
thus  renders  them  more  visible. 

Finally,  it  may  be  affirmed  that  there  often  exists  a  need 
of  making  objects  which  are  too  dark  more  transparent  by 
means  of  a  fluid  which  permeates  them  un>  Dually,  so  that 


OF   MICROSCOPIC   OBJECTS.  7 

the  tissues  are  thereby  as  it  were  "  differentiated,"  yet  not 
altered  in  any  material  degree.  This  may  be  effected  by 
solutions  of  gum,  sugar,  glycerine,  and  creosote,  if  the 
tissues  are  moist.  If  dry,  then  turpentine,  Canada  balsam, 
benzine  or  benzole,  and  the  essential  oils  of  cloves,  anise, 
and  cassia,  may  be  employed. 

2ND  DIVISION. 

Under  the  second  division  of  our  subject  come  staining 
fluids. 

Many  of  these  will  be  found  mentioned  in  the  body  of  this 
work.  They  comprise  carmine  solutions,  both  acid  and 
alkaline ;  aniline  colours,  indigo,  carmine,  hasmatoxyline, 
&c ,  formulas  for  the  use  of  which  are  given.  To  these  Frey 
adds,  blue  tingeing-  by  molybdate  of  ammonia,  and  double 
staining  by  carmine  and  picric  acid. 

A  neutral  solution  of  the  molybdate  of  ammonia  of  the 
strength  of  5  per  cent,  gives  a  blue  tint  to  nerve-tissue, 
lymphatic  glands,  and  ciliated  epithelial  cells,  after  macera- 
tion for  24  hours  in  the  light. 

For  double  staining  by  carmine  and  picric  acid  he  recom- 
mends a  mixture  containing — 

1  part  creosote, 
10  parts  acetic  acid, 
20  parts  water. 

Soak  the  tissues  in  this  solution  while  boiling  for  abont  a 
minute,  then  dry  for  two  days.  Make  thin  sections  of  them, 
immerse  for  an  hour  in  water  faintly  acidulated  with 
acetic  acid,  and  then  wash  in  distilled  water.  Next  place 
them  in  a  very  dilute  watery  solution  of  ammoniacal  car- 
mine, wash  again  in  water,  and  place  in  a  solution  of  picric 
acid  in  water,  the  strength  of  which  will  vary  according  to 
circumstances.  The  sections  are  then  to  be  placed  on  a 
slide,  superfluous  acid  allowed  to  drain  off,  and  a  mixture  of 
4  parts  creosote  to  1  of  old  resinous  turpentine  dropped  on 


8  PREPARATION   AND   MOUNTING 

them.  In  about  half  an  hour  they  will  become  transparent, 
and  may  be  mounted  in  Canada  balsam. 

"A  peculiar  effect  is  thus  obtained.  Epithelial  and 
glandular  cells,  muscles,  and  the  walls  of  vessels  show  a 
yellowish  colour,  with  reddened  nuclei,  while  the  connective 
tissue  is  not  coloured  by  the  picric  acid,  and  only  presents 
the  carmine  colour." 

Another  mode  of  effecting  the  above  is  by  adding  to  a 
saturated  and  filtered  solution  of  picric  acid  in  water,  a 
strong  ammoniacal  solution  of  carmine,  drop  by  drop,  until 
neutralization  takes  place.  Sections  may  be  soaked  in  this 
solution,  more  or  less  dilute,  for  a  sufficient  time,  and 
treated  as  in  the  previous  method. 

The  other  staining  agents  are : — nitrate  of  silver,  osmic 
acid,  chloride  of  gold,  chloride  of  gold  and  potassium,  proto- 
chloride  of  palladium.  These  are  to  be  made  into  weak 
solutions  in  distilled  water,  in  which  the  tissues,  in  section 
or  otherwise,  are  to  be  placed,  and  then  exposed  to  light  for 
a  sufficient  time. 

L^ber  recommends  a  mode  of  staining  by  Prussian  blue, 
as  follows : — Immerse  the  specimen  in  a  weak  solution 
of  a  protosalt  of  iron  for  five  minutes,  more  or  less, 
according  to  size  or  the  thinness  of  the  section.  Then 
wash  and  move  it  to  and  fro  for  a  few  minutes  in  a 
1  per  cent,  solution  of  ferro-cyanide  of  potassium  until  it 
assumes  an  intense  and  uniform  blue  colour.  Then  wash 
in  water,  soak  in  alcohol,  and  mount  as  usual.  The  effect 
is  that  of  partial  tingeing ;  the  colour  penetrates  very 
deeply,  and  the  tissue  may  be  subsequently  stained  with 
iodino,  carmine,  or  fuchsine.  This  method  has  been  used  for 
the  cornea  of  the  frog. 

Iodine  1  part,  with  3  of  iodide  of  potassium,  dissolved  in 
500  of  water,  may  be  used  for  tingeing  of  a  brown  colour 
animal  cells,  as  well  as  all  amyloid  substances,  animal  or 
vegetable,  sulphuric  acid  being  added. 


OF   MICROSCOPIC   OBJECTS.  9 

3BD   DIVISION. 

Under  the  third  division  of  our  list  may  be  ranged  the 
following  agents  : — alcohol,  solutions  of  chromic  acid,  bi- 
chromate of  potash,  hyperosmic  acid,  chloride  of  palladium, 
bichloride  of  mercury  (in  Goadby's  solution),  and  tannin,  or 
the  substance  may  be  dried  in  thin  layers  or  small  pieces, 
either  spontaneously  or  in  vacuo,  or  by  carefully  regulated 
heat ;  in  some  cases  it  may  be  boiled,  or  it  may  be  frozen. 

Alcohol  is,  on  the  whole,  the  best  and  most  convenient  of 
the  hardening  agents.  It  acts  by  abstracting  water  and 
coagulating  albumen,  and  its  uses  as  a  preservative  fluid 
per  se  are  well  known.  It  enters  also  into  many  of  the 
preservative  fluids,  and  is  especially  convenient  and  useful 
when  it  is  desired  to  mount  specimens  quickly  out  of  watery 
fluids  in  Canada  balsam,  without  drying  them  previously. 
After  a  longer  or  shorter  soaking  in  it,  according  to  their 
size  or  thinness,  preparations  may  be  at  once  placed  in  tur- 
pentine, and  then  easily  and  speedily  put  np  for  examina- 
tion in  balsam. 

Dr.  Beale  recommends  a  mixture  of  alcohol  and  a  solu- 
tion of  caustic  soda  for  the  preservation  of  delicate  tissues. 
He  observes,  "  that  alcohol  alone  tends  to  coagulate  albu- 
minous textures  and  render  them  opaque,  at  the  same  time 
that  it  hardens  them.  The  alkali,  on  the  other  hand,  will 
render  them  soft  and  transparent,  and  would  dissolve  them 
if  time  were  allowed.  These  two  fluids,  in  conjunction, 
harden  the  texture,  and  at  the  same  time  make  it  clear  and 
transparent." 

Chromic  acid  in  solution,  O25 — 0'5  to  1  and  2  per  cent, 
of  distilled  water  is  much  used.  On  account  of  its  deli- 
quescence, it  is  most  conveniently  kept  in  a  saturated  solu- 
tion, which  may  be  diluted  as  desired;  and  very  often  the 
weaker  this  solution  the  better.  When  it  has  had  the  de- 
sired effect  on  the  tissue,  the  preparation  should  be  removed 
into  diluted  alcohol,  on  account  of  the  readiness  with  which 
fungi  and  confervoid  growths  are  formed  in  chromic  acid 


10  PKEPARATION   AND   MOUNTING 

solutions.  There  are  some  precautions  needed  for  perfect 
success  with  this  agent,  for  which  the  reader  is  referred  to 
Frey's  "  Microscopic  Technology." 

Bichromate  of  potash,  in  solutions  of  similar  strength  to 
those  of  chromic  acid,  may  be  used  in  the  same  way,  but  is 
far  slower  in  producing  its  effect,  and  therefore  inferior  in 
the  opinion  of  many.  Strieker,  however,  says,  "  that  it  has 
the  great  advantage  that  tissues  saturated  with  it  do  not 
become  friable,  and  that  the  time  occupied  by  this  agent, 
as  well  as  by  the  preceding,  may  be  much  shortened  by  re- 
moving the  preparation  into  alcohol  for  twenty-four  hours." 

It  is  always  advisable  to  divide  the  substances  to  be  har- 
dened into  portions  as  small  as  convenient,  since  the  larger 
often  putrefy  in  the  centre,  though  they  harden  at  the  sur- 
face. It  is  quite  certain  that  many  of  the  more  delicate 
structures,  such  as  the  rods  of  the  cochlea  of  the  ear 
(Pritchard),  those  of  the  eyes  of  insects,  &c.,  are  better 
prepared  with  this  than  by  the  preceding  agent.  One  great 
element  of  success  in  these  two  processes  is,  that  the  volume 
of  the  solution  should  be  very  large  in  proportion  to  the 
size  of  the  object;  another,  that  the  action  should  be 
commenced  with  a  weak  solution,  and  continued  with  a 
stronger. 

It  sometimes  happens  that  objects  may  be  hardened  too 
much  by  these  solutions,  though  there  is  less  risk  by  the 
bichromate  of  potash.  In  such  cases  Frey  recommends  that 
they  be  soaked  in  glycerine  for  a  few  days,  and  even  that  it 
be  added  to  the  solutions  at  first.  He,  with  Deiters,  Arnold, 
Schultze,  and  Kiihne,  claims  for  these  solutions  an  effect  of 
the  most  important  kind,  viz.,  that  of  "  preserving  the  finest 
textural  relations,  while  exerting  a  somewhat  macerating 
action  on  them,  so  that  very  delicate  organizations,  especially 
in  nerve  tissues,  may  be  made  visible  which  were  previously 
hidden,  or  not  visible  in  examination  of  the  fresh  tissue." 

Hyperosmic  acid  and  chloride  of  palladium  are  sometimes 
used  for  this  purpose  also.  Their  solutions  may  contain 
from  one-fifth  to  one-tenth  per  cent,  of  distilled  water. 


OF  MICROSCOPIC  OBJECTS.  11 

Bichloride  of  mercury  acts,  in  hardening  tissues  (like 
most  of  the  preceding,  probably),  by  combining  and  forming 
an  insoluble  compound  with  their  albuminoid  elements.  It 
is  not  much  employed  for  this  purpose,  but  is  principally 
of  use  in  certain  preservative  solutions  mentioned  elsewhere 
in  these  pages. 

Tannic  acid  forms  insoluble  compounds  with  a  great 
variety  of  organic  and  especially  animal  substances,  as  solu- 
tions of  starch  and  gelatine,  solid  muscular  fibre  and  skin, 
&c.,  which  then  acquire  the  power  of  resisting  putrefac- 
tion. It  scarcely  colours  animal  membrane.  Dr.  Beale 
says  that  its  action  upon  red  blood  corpuscles  is  "  very 
peculiar."  The  solution  used  is  three  grains  to  an  ounce  of 
water.  Other  uses  of  tannin  (tannic  acid)  will  be  found 
elsewhere  in  this  work,  and  the  intelligent  student  will  easily 
thence  infer  its  action  and  properties. 

Drying  may  be  effected  either  in  a  current  of  warm  dry 
air,  or  under  a  bell-glass  over  sulphuric  acid,  or  over  a  layer 
of  parched  oatmeal ;  or  a  cheap  form  of  water  bath  may  be 
employed,  such  as  will  be  found  described  in  this  work. 
Another  very  speedy  method  is  to  soak  the  specimen  in 
strong  alcohol  for  a  sufficient  time,  remove  it,  and  expose  to 
a  current  of  warm  dry  air. 

Boiling. — Tissues  may  be  hardened  by  boiling  in  a  fluid 
consisting  of  8  parts  water,  1  part  creosote,  and  1  part 
vinegar,  for  two  or  three  minutes.  They  may  then  be  laid 
out  to  dry.  After  two  or  three  days  they  acquire  a  firm- 
ness admirably  adapted  for  section ;  but  if  they  remain  too 
long  uncut  they  become  of  a  consistence  unfit  for  that  pur- 
pose. On  the  whole,  boiling  is  not  to  be  recommended, 
though  Strieker  says  that  it  has  its  occasional  uses. 

Freezing  may  be  employed  for  otherwise  unmanageable 
structures,  such  as  brain,  spinal  cord,  &c.  (though  there 
seems  to  be  an  objection  of  a  theoretical  kind  to  this  use  of 
it,  viz.,  that  it  may  injure  or  alter  the  cells),  or  other  tissues 
which  will  not  admit  the  use  of  chromic  acid,  or  which  it  may 
be  desired  to  view  under  other  aspects. 


12  PKEPARATION  AND  MOUNTING 

The  writer  has  little  or  no  experience  of  this  plan,  he 
therefore  quotes  from  Frey  as  follows  : — 

"  Tne  preparation  is  allowed  to  freeze  (by  contact,  it  is 
presumed,  with  a  freezing  mixture  or  solution)  until  it  as- 
sumes a  consistency  which  will  permit  fine  sections  to  be 
made  with  a  cooled  razor.  The  object  is  more  convenient  to 
handle  if  it  is  allowed  to  freeze  on  a  piece  of  cork.  Nerves 
and  muscles  have  been  treated  in  this  manner  with  good 
results.  Glands  (salivary),  livers,  spleens,  the  lungs,  skin, 
and  the  bodies  of  embryos  (see  Beale's  process  for  the  same 
in  this  work),  also  ganglia,  afford  excellent  appearances. 
Indifferent  (or  neutral)  media,  such  as  iodine  serum,  are  to 
be  used  in  examining  such  sections.  Or  the  preparation  may 
be  held  in  paraffine  wax  (diluted  or  not  with  oil),  or  tallow, 
which  have  been  melted,  and  the  object  suspended  or 
plunged  in  them  until  they  cool,  and  the  cooling  may  be 
carried  further,  if  needed,  by  freezing." 

In  reference  to  this  subject,  Mr.  Kesteven  informs  the 
author  that  he  has  found  the  paraffine  composition  more 
useful  for  brain  than  spinal  cord.  The  former  can  be  cut 
into  any  angular  shape,  and  be  so  held  steady  for  slicing; 
but  the  cord,  being  round,  becomes  loosened  in  its  setting  of 
wax  (or  paraffine),  and  revolves  with  the  pressure  of  the  knife. 
For  either  brain  or  cord  he  prefers  hand-cutting  with  a  very 
sharp  razor,  after  the  manner  of  Lockhart  Clarke  (see  Mr. 
Kesteven's  paper  in  St.  Bartholomew's  Hospital  Reports). 
If  many  sections  are  to  be  made  from  a  brain,  machine- 
cutting  saves  much  time.  The  razor  should  have  some 
spirit  of  wine  dropped  on  it,  so  as  to  prevent  the  sections 
adhering.  The  cutting  machines  are  generally  graduated 
(by  a  screw  and  index)  on  the  upward  movement,  so  as  to 
enable  one  to  judge  of  the  thickness  of  the  section  ;  but  as 
the  brain  substance  and  paraffine  are  both  yielding  to  a  cer- 
tain extent,  the  reading  mast  be  taken  with  allowance. 


OF   MICROSCOPIC   OBJECTS.  13 

4iH  DIVISION. 

This  includes  glycerine,  liquor  potassae  and  sodae,  heat  (as 
regards  some  substances),  maceration  (carried  to  incipient 
putrescence),  nitric  and  chlor-hydric  acids,  either  pure  or 
dilute  (in  the  case  of  bones,  nails,  &c.). 

The  writer  is  in  doubt  whether  glycerine  ought  or  not  to 
be  included  under  this  section  or  the  first,  its  uses  and 
effects  being  so  various  and  interesting.  Indeed,  there  is 
scarcely  any  agent  to  which  histology  is  more  indebted  for 
its  present  status  and  progress,  since  there  is  now  no  doubt 
that  elementary  tissue  can  be  more  readily  discriminated  in 
this  medium — perhaps,  too,  Toy  it — than  any  other.  It  has 
also  the  valuable  property  of  preserving  the  tissues,  if  it  be 
not  too  much  diluted,  and  even  then  it  is  generally  effectual 
if  camphor  water  be  employed  as  the  diluent.  The  strongest 
and  best  glycerine  should  always  be  employed.  The  first 
effect  on  tissues  immersed  in  it  is  that  they  shrink,  owing 
to  the  abstraction  of  their  water ;  but  Dr.  Beale  speaks  in 
the  highest  terms  of  its  uses  and  advantages,  and  declares 
that  the  tissues  gradually  regain  their  original  volume  if 
left  in  it  for  a  sufficient  time.  They  then  soften,  and  even 
swell  up.  His  practice  is  first  to  immerse  the  specimen  in 
weak  glycerine  solution,  and  then  gradually  to  increase  the 
density  of  the  fluid.  He  recommends,  also,  "  in  order  that 
tissues  may  be  uniformly  permeated  with  a  fluid  within  a 
very  short  time  after  the  death  of  an  animal,  that  the  fluid 
should  come  quickly  in  contact  with  every  part  of  the  texture." 
This,  he  says,  may  be  effected  in  two  ways,  by 

A.  Soaking  very  thin  pieces  in  the  fluid; 

B.  By  injecting  the  fluid  into  the  vessels  of  the  animal. 

He  thinks  that  these  properties  more  particularly  apper- 
tain to  glycerine  than  to  any  other  medium,  and  affirms 
that "  cerebral  tissues,  delicate  nervous  tissues  like  the  retina 
or  the  nerve-textures  of  the  internal  ear,  may  be  saturated 
with  it,  and  dissection  then  carried  to  a  degree  of  minuteness 


14  PREPARATION    AND   MOUNTING 

impossible  in  any  other  medium.  All  that  is  required  is, 
that  the  strength  of  the  fluid  should  be  increased  very 
gradually  until  the  whole  tissue  is  thoroughly  penetrated  hy 
the  strongest  that  can  be  obtained ;"  and  "  that  thus  very 
hard  textures  may  be  softened,  so  that  by  gradually  increas- 
ing pressure  and  careful  manipulation  exceedingly  thin 
layers  can  be  obtained,  without  the  relation  of  the  anatomi- 
cal elements  to  each  other  being  much  altered,  or  any  of  the 
tissues  destroyed."  He  also  takes  occasion  to  observe,  "  that 
tissues  immersed  in  water  are  destroyed  by  even  moderate 
pressure ;  but  that  in  a  viscid  medium  (such  as  glycerine  or 
syrup)  the  requisite  pressure  can  be  borne  not  only  without 
injury  or  impairment  of  the  discrimination  of  their  parts, 
but  with  advantage  to  their  detail."  One  very  great  advan- 
tage which  results  from  the  use  of  glycerine  for  the  prepara- 
tion of  textures  is,  that  however  they  may  swell  in  it  after 
prolonged  immersion,  a  sufficient  soaking  in  water  will 
always  restore  them  to  their  normal  condition.  Another  is, 
that  on  account  of  its  very  high  refractive  power,  it  is 
peculiarly  fitted  for  the  preparation  of  structures  to  be  in- 
vestigated by  polarized  light,  with  the  same  advantage  as  in 
the  preceding  case,  that  they  are  still  amenable  to  all  other 
modes  of  inquiry. 

The  caustic  alkalies — potash,  soda,  and  ammonia,  are 
solvents  of  all  animal  textures  except  chitine,  and  perhaps 
bone.  As  in  nearly  all  cases  a  softening  action,  with  little 
or  no  alteration  of  tissue,  precedes  the  solvent  action,  these 
agents,  and  especially  the  first  two,  have  their  uses.  Under 
their  influence  "  a  condition  is  induced  very  favourable  to 
the  imbibition  of  water,  which  afterwards  penetrates  very 
rapidly,  so  that  cells  swell  up  and  burst."  They  may  be 
used  either  with  or  without  heat,  and  more  or  less  dilute. 
There  is  one  disadvantage  attending  their  use,  that  objects 
can  with  difficulty  be  preserved  after  soaking  in  them. 

Heat,  applied  either  by  the  aid  of  hot  water  or  steam,  or 
the  sand-bath,  or  a  bath  of  fusible  metals,  or  of  melted  leud, 
is  a  very  efficient  means  of  softening  horny  substances,  whale- 


OF   MICROSCOPIC   OBJECTS.  15 

bone,  &c.,  and  rendering  them  plastic.  Very  thin  laminae  of 
these  substances  may  also  be  procured  by  the  employment 
of  a  well-sharpened  scraper,  such  as  that  used  by  cabinet- 
makers. This  plan  applies  more  to  longitudinal  than  to 
transverse  sections ;  yet  even  the  latter  may  be  obtained  by 
fixing  the  object  while  soft  in  a  piece  of  hard  wood,  and 
scraping  both  together.  Long  continued  slow  boiling  softens 
and  eventually  disintegrates  nearly  all  animal  and  vegetable 
tissues.  Muscular  fibre  and  many  other  textures  may  thus 
be  isolated,  such  as  spiral  vessels,  &c.,  in  vegetables. 

Prolonged  maceration  in  water,  for  the  preparation  of. 
anatomical  structures,  generally  bony,  is  a  process  too  well 
known  to  need  description  here.  The  addition  of  very 
dilute  nitric,  hydrochloric,  and  acetic  acids  is  much  em- 
ployed for  the  separation  of  muscular  fibres,  both  striated 
and  smooth.  Two  or  three  days  are  required,  or  even  more. 

Nails  may  be  softened  very  quickly  by  hot  concentrated 
sulphuric  acid — or,  still  better,  by  liquor  potasses,  strength 
about  25  to  27  per  cent.— so  as  to  show  isolated  and  dis- 
tended cells  by  solution  of  the  intercellular  substance. 

Bones  are  softened,  i.e.  decalcified,  by  boiling  or,  still 
better,  by  slow  maceration  in  weak  solutions  of  nitric  and 
hydrochloric  acids,  by  the  action  of  which  the  phosphate 
and  carbonate  of  lime  may  be  entirely  removed.  This  pro- 
cess isolates  the  animal  matter,  i.e.  the  osseine — sometimes 
miscalled  gelatine — with  all  its  peculiar  fibres  and  processes. 
But  bones  may  be  treated  in  another  way,  so  as  to  show  or 
isolate  the  bone  corpuscles  with  their  processes,  by  removal 
or  destruction  of  the  intercellular  substance.  Though  this 
can  scarcely  be  called  softening  them,  yet  it  may  be  most 
fitly  mentioned  here.  For  this  purpose,  a  Papin's  digester 
is  necessary.  When  the  boiling  of  bones  has  been  for  a  long 
time  carried  on  by  means  of  one  of  these  machines,  they 
seem  to  be  dissolved ;  but  on  examination  a  coarse  powder, 
consisting  of  the  isolated  corpuscles  and  their  processes,  is 
found  at  the  bottom  of  the  vessel,  which  will  amply  repay 
the  trouble  of  examination. 


16  PKEPAKATION   AND   MOUNTING 

Teeth  may  be  treated  in  the  same  manner  as  bone?,  except 
for  the  examination  of  the  enamel,  which  is  best  effected  by 
sections  and  grinding.  For  that  purpose  developing  teeth 
should  be  chosen,  as  in  them  the  enamel  prisms  are  most 
easily  isolated. 

5m  DIVISION. 

As  the  solution  of  animal  and  vegetable  tissues  generally 
means  the  confusion  or  destruction  of  their  histological 
elements,  not  much  can  or  need  be  said  of  it  here,  except 
that  it  may  be  as  well  to  indicate  the  special  solvents  and 
tests  of  the  special  components  of  all  tissues,  since  it  is  upon 
a  correct  knowledge  and  appreciation  of  the  degrees  and 
differences  of  the  action  of  these,  that  effective  histological 
research  must  chiefly  depend. 

Albumen,  when  pure,  is  nearly  insoluble  in  water,  wholly 
so  when  coagulated  by  heat.  In  dilute  caustic  alkali  it 
dissolves  with  facility.  Solution  of  nitrate  of  potash,  acetic 
and  tri-basic  phosphoric  acids,  and  pepsine,  dissolve  the  pur- 
est form  of  albumen  procured  from  white  of  egg. 

Fownes  observes,  "  that  it  must  be  remembered  that  a 
considerable  quantity  of  alkali  and  very  minute  quantities 
of  the  mineral  acids,  prevent  coagulation  by  heat,  and  that 
the  addition  of  acetic  acid,  indispensable  to  the  test  by  mer- 
cury, produces  the  same  effect." 

Fibrine  of  blood  is  insoluble  in  both  hot  and  cold  water, 
but  is  partly  dissolved  by  long-continued  boiling.  Fresh 
fibrin e,  wetted  with  concentrated  acetic  acid,  forms  after 
Borne  hours  a  transparent  jelly,  which  slowly  dissolves  in 
water.  Very  dilute  caustic  alkali  dissolves  fibrine  completely. 
Phosphoric  acid  produces  a  similar  effect.  Fibrine  of  flesh, 
which  is  not  identical  with  that  of  blood  (Liebig),  is  soluble 
in  cold  water  containing  one-tenth  of  hydrochloric  acid. 

Casein  is  only  soluble  in  water  in  the  presence  of  free 
alkali  in  very  small  quantities.  It  is  partly  soluble  also  in 
very  dilute  acids. 


or  MICROSCOPIC  OBJECTS.  17 

Gelatin,  chondrin,  and  osseine  are  the  result  of  the  boiling 
of  animal  membranes,  skin,  tendons,  and  bones,  respectively 
at  a  high  temperature  for  a  sufficient  time.  They  are 
insoluble  in  cold  water,  but  easily  dissolved  by  the  use  of 
heat.  Alcohol,  corrosive  sublimate  in  excess,  nitrate  of 
mercury,  and,  most  characteristically,  tannin,  precipitate 
gelatine — the  latter  when  it  is  very  largely  diluted. 

"  Skin  and  tendons  contain  a  substance  which  resists  the 
action  of  boiling  water  for  many  hours.  It  is  insoluble  in 
cold  concentrated  acetic  acid,  but  by  long-continued  boiling 
in  it,  is  gradually  dissolved,  and  more  easily  in  hydrochloric 
acid."  (Fownes.) 

Horny  substance — keratin,  found  in  hair,  nails,  feathers, 
and  epithelium,  is  obtained  by  finely  dividing  them,  treat- 
ing them  with  hot  water,  and  afterwards  by  boiling  alcohol 
and  ether.  The  horny  substance  is  then  very  soluble  in 
caustic  potash. 

Of  bones  we  have  already  spoken. 

It  has  been  mentioned  elsewhere  in  this  work,  that  all 
the  internal  organs  of  insects  may  easily  be  dissolved  out  by 
boiling  in  liquor  potassae,  leaving  their  external  chitinous 
structures,  limbs,  &c.,  unaffected.  Bat  this  is  a  proceeding 
much  to  be  deprecated,  for  various  reasons  which  it  is 
scarcely  necessary  to  give  here.  It  is  far  better  to  treat 
them  in  another  way,  by  which  these  organs  may  be  ex- 
amined in  situ,  at  least  to  a  very  great  extent,  as  will 
presently  be  shown. 

The  parenchyma  of  leaves  and  many  other  vegetable 
structures  may  be  decomposed  by  prolonged  maceration  in 
water,  and  then  easily  be  washed  away.  Nitric  acid,  vary- 
ingly  diluted,  will  produce  the  same  effect  more  speedily,  the 
objects  not  requiring  the  same  amount  of  bleaching  subse- 
quently. But  by  far  the  best  and  most  speedy  method  is, 
to  place  them  in  the  liquid  manure  tank  of  the  gardener 
for  a  sufficiently  long  maceration.  The  results  of  this  plan 
are  exquisitely  beautiful. 


18  PREPARATION  AND  MOUNTING 

GTH  DIVTSION. 

The  proper  solvents  of  calcareous  animal  matters  are 
nitric,  hydrochloric,  and  sulphuric  acids.  The  earth  of 
bones  consists  of  a  combination  of  two  tribasic  phosphates 
of  lime,  both  of  which  are  entirely  soluble  in  nitric  and 
hydrochloric  acids.  Sulphuric  acid  abstracts  a  part  of  the 
lime  of  bones,  leaving  a  superphosphate — a  substance  much 
used  in  agriculture  as  a  manure.  Fluoride  of  calcium, 
existing  in  small  quantity  in  bones,  but  in  larger  in  the 
enamel  of  teeth  (and  of  the  ganoid  scales  of  fish  ?),  is  de- 
composed by  sulphuric  acid,  which  combines  with  the  cal- 
cium, allowing  the  hydrofluoric  acid  to  fly  off  in  a  gaseous 
state.  Carbonate  of  lime  dissolves  in  nitric  and  hydro- 
chloric acids.  The  shells  of  mollusca,  and  testas  of  echino- 
dermata,  consisting  principally  of  carbonate  of  lime,  are  also 
soluble  in  the  same  acids,  as  well  as  those  of  nummulites 
foraminifera,  &c.,  which  have  been  infiltrated  with  siliceous 
matter.  These  present  the  most  beautiful  "  casts,"  which 
are  exactly  of  the  shape  of  the  Sarcode  body  and  canal  sys- 
tem, thus  enabling  their  internal  organs  to  be  studied  with 
much  accuracy.  Dr.  Carpenter  says  that  they  are  of  "  won- 
derful completeness." 

?TH  DIVISION. 

Silica  is  nearly  altogether  insoluble  in  water,  but  dissolves 
freely  in  strong  alkaline  solutions.  Its  only  acid  solvent  is 
hydrofluoric  acid.  Its  combinations  with  a  larger  proportion 
of  alkali  are  soluble  in  water,  and  from  such  solutions  silica 
may  be  precipitated  in  a  gelatinous  or  colloid  form  by 
acids,  or  separated  by  dialysis,  in  the  form  of  colloid  silica. 
This  substance  may  be  used  for  procuring  certain  modifica- 
tions of  crystals  of  salts  for  the  polariscope,  such  as  sulphate 
of  magnesia,  sulphate  of  copper,  boraoic  acid,  sulphate  of  zinc, 
&c.  In  its  combination  with  a  smaller  proportion  of  alkali, 
forming  glass,  it  is  attacked  by  hydrofluoric  acid  and  its 
vapour,  and  advantage  may  be  taken  of  this  property  to 


OF   MICROSCOPIC   OBJECTS.  19 

engrave  names,  numbers,  &c.,  neatly  upon  slides,  for  classifi- 
cation in  the  cabinet.  The  glass  to  be  engraved  must  be 
coated  with  an  etching  ground  of  oily  varnish  or  wax,  and 
the  necessary  writing  effected  upon  it  by  a  point,  which 
must  pierce  through  the  protective  material.  A  shallow 
basin,  made  by  bending  up  the  edges  of  a  piece  of  sheet-lead, 
is  then  prepared,  a  little  powdered  floor  spar  placed  in  it, 
and  enough  sulphuric  acid  added  to  form  a  thin  paste.  The 
glass  is  then  placed  in  any  convenient  way  over  the  basin, 
the  waxed  side  downwards.  A  gentle  heat  is  next  applied, 
whereby  the  vapour  of  hydrofluoric  acid  is  disengaged.  This 
acts  upon  the  glass  exposed  by  the  point  in  a  very  few 
minutes,  removing  a  portion  of  its  surface.  The  wax  must 
then  be  removed  by  turpentine.  If  the  lines  which  result 
are  then  rubbed  over  with  any  coloured  .varnish,  and  the 
varnish  gently  wiped  off  by  a  soft  piece  of  rag,  a  sufficient 
portion  will  most  probably  remain  in  the  etched  marks  to 
render  them  easily  visible  and  legible.  Of  course  it  will  be 
as  well  to  prepare  many  slides  in  this  way  at  once.  It  is  not 
necessary  to  coat  the  whole  surface  of  the  slides  with  the 
protective  varnish,  if  the  leaden  basin  be  covered  with  a 
thin  piece  of  wood  or  sheet-lead  perforated  with  holes 
slightly  larger  than  the  surface  to  be  etched,  over  which 
holes  the  slides  must  be  inverted  for  a  sufficient  time.  This 
latter  hint  applies  more  particularly  to  finished  slides  requir- 
ing to  be  labelled. 

STH  DIVISION. 

The  proper  solvents  of  the  fixed  oily  and  fatty  matters 
are  ether,  benzole  (or  benzine),  turpentine,  and  the  essen- 
tial oils  generally.  Castor  oil  is  nearly  the  only  one  which 
is  soluble  in  alcohol,  the  rest  being  only  slightly  so.  They 
are  all  capable  of  saponification  with  caustic  alkalis,  and  so 
become  indirectly  soluble  in  soft  or  distilled  water,  other- 
wise they  are  wholly  insoluble  in  it. 

The  volatile  or  essential  oils  mix  in  all  proportions  with 
fatty  oils,  and  are  wholly  soluble  in  ether  and  alcohol. 

c2 


20  PREPARATION  AND  MOUNTING 

Camphor  dissolves  in  a  only  very  small  proportion  in  water, 
but  freely  in  alcohol,  ether,  and  strong  acetic  acid. 

9iH  DIVISION. 

It  is  by  no  means  intended  to  speak  here  of  the  general 
properties  and  uses  of  polarized  light.  Bat  in  relation  to 
its  special  powers  in  the  "  differentiation  "  of  tissues,  there 
is  very  much  to  be  learned.  To  be  fitted  for  examination 
by  this  method,  objects  must  be  made  more  or  less  trans- 
parent or  translucent;  and  in  effecting  this  it  is  advisable, 
perhaps  necessary,  to  employ  media  of  high  refractive  power. 
Even  when  so  prepared,  it  may  be  further  necessary  in  some 
cases  to  employ  selenite  or  mica  films,  still  more  to  enhance 
their  colour.  ITot  the  least  indication  can  be  afforded  to  the 
observer  as  to  what  colours  he  should  employ  generally,  yet 
it  is  a  matter  of  frequent  observation  that  what  are  called 
"  neutral  tints  "  are  to  be  preferred,  such  as  result  from  the 
judicious  use  of  compound  selenite  stages  adjusted  properly 
for  that  special  effect. 

The  media  most  suitable  for  the  preparation  of  objects  to 
be  examined  in  this  way  are  glycerine,  syrup,  turpentine, 
dammar  and  benzole — or  the  latter  alone,  Canada  balsam, 
and  the  essential  oils.  Of  course  sections  must  be  made  of 
tissues  otherwise  too  thick.  Of  the  advantages  of  employing 
the  first  of  these  we  have  already  spoken;  but  to  these  must 
be  added  this  important  one,  that  it  does  not  spoil  the  object 
for  examination  by  other  methods,  if  the  glycerine  be  soaked 
out  by  maceration  in  water;*  and  this  is  true  also  of  syrup, 
though  it  is  far  less  useful.  For  preparation  by  the  other 
methods,  tissues  must  have  been  soaked  in  alcohol,  and  then 
removed  into  the  turpentine,  &c. 

For  the  examination  of  insects  by  polarized  light,  two 
preliminaries  are  necessary.  Firstly,  that  they  be  made 
transparent  or  translucent  by  prolonged  soaking  in  one  of 
the  above-named  media,  preferably  in  turpentine  or  the 
essential  oils,  or  benzole.  Secondly,  that  as  in  (mostp) 
many  of  them  their  chitinous  case  is  too  deeply  coloured  for 


OP   MICROSCOPIC   OBJECTS.  21 

any  amount  of  soaking  to  render  them  sufficiently  trans- 
parent, some  bleaching  process  should  he  premised.  A  for- 
mula for  such  a  process  may  be  found  in  another  part  of 
this  work,  where  the  preparation  of  the  antennas  of  insects 
is  described.  If  that  should  not  prove  successful,  some 
modification  will  easily  occur  to  the  student.  Of  course  it 
is  not  all  insects  that  can  be  treated  in  this  way,  the  size 
and  deep  colour  of  very  many  quite  preventing  a  good 
result ;  but  when  they  have  been  successfully  prepared  by 
any  of  the  methods  of  which  we  have  spoken,  it  is  then 
possible  to  discriminate  their  internal  organs  by  the  differ- 
ences of  colour  which  they  present.  The  use  of  the  binocular 
microscope,  and  of  objectives  of  low  angular  aperture,  will 
also  much  facilitate  this  mode  of  examination,  by  increasing 
the  depth  of  focus,  and  enabling  the  organs  to  be  seen  more 
or  less  in  connection  with  each  other,  even  if  they  be  super- 
posed. It  is  also  possible  to  examine  the  muscles  of  the 
limbs  and  bodies  of  insects,  so  as  to  decide  upon  their  forma- 
tion, origin,  and  insertion,  and  probable  mode  of  action ;  and 
this  is  only  one  of  many  such  uses.  What  a  mistake  must 
it  be,  then,  to  prepare  insects  for  mounting  by  boiling  in 
liquor  potassae,  and  so  dissolving  out  their  viscera,  and 
squeezing  them  flat! 

In  the  case  of  living  insects,  especially  those  of  the  more 
transparent  salt  and  fresh  water  species,  the  results  of  their 
examination  by  polarized  light  are  exquisitely  beautiful  and 
interesting,  because  their  organs  and  circulation  may  be 
more  clearly  discriminated  while  in  motion. 

lOrn  DIVISION. 

Electricity  has  been  employed  in  histology  partly  for  its 
electrolytic  effects,  but  chiefly  as  a  means  of  producing 
certain  variations  of  temperature  in  objects  under  examina- 
tion. Strieker  says  "  that  the  tissues  become  altered  by  it 
as  they  would  be  were  they  subjected  to  the  action  of  weak 
acids  or  alkalias,"  and  he  describes  a  rather  complicated 
apparatus  for  this  purpose,  of  which  it  is  impossible  to  give 


22  PREPARATION   AND   MOUNTING 

an  account  here ;  but  the  author  believes  that  most,  if  not 
all,  of  the  same  effects  may  be  produced  by  the  employment 
either  of  a  thick  plate  of  metal  placed  upon  the  stage,  or  of 
a  thin  water-bath,  which  may  be  heated  by  a  spirit  or  gas 
flame,  after  the  glass  slide  shall  have  been  placed  on  it. 
They  should  both  be  properly  fitted  with  thermometers. 

Of  the  decomposition  of  salts  by  electricity,  and  their  re- 
duction to  the  metallic  state,  it  is  not  necessary  to  speak 
here,  but  such  effects  are  very  beautiful,  and  the  resulting 
crystalization  may  easily  be  watched. 

Dr.  Beale  speaks  very  favourably  of  the  inverted  micro- 
scope devised  by  Dr.  Lawrence  Smith,  U.S.A.,  by  which 
objects  may  be  viewed  from  their  under  instead  of  from  their 
upper  surface,  and  at  the  same  time  heated  (or  re-agents 
applied  to  them)  without  any  risk  of  dimming  or  injuring 
the  object-glass  by  vapours  thus  raised.  The  optical  part 
is  so  fitted  to  the  base  that  it  may  be  drawn  away  from  be- 
neath the  stage  (to  make  room  for  the  application  of  the 
lamp,  or)  for  the  sake  of  changing  the  powers. 

HTH  DIVISION. 

It  is  evident  that  in  all  these  plans  an  amount  of  evapo- 
ration is  constantly  going  on,  which  will  eventually  dry  and 
so  spoil  the  object,  unless  obviated.  Frey,  therefore,  describes 
a  "  moist  chamber "  invented  by  E/ecklinghausen  for  this 
purpose.  It  consists  of  a  glass  ring,  more  or  less  high, 
which  has  been  cemented  by  its  edge  to  a  broad  glass  slide. 
A  tube  of  thin  rubber  is  then  firmly  fastened  about  the  ring. 
The  upper  end  of  this  tube  is  also  fastened  around  the  tube 
of  the  microscope.  In  order  to  keep  the  place  thus  enclosed 
saturated  with  moisture,  some  small  pads  of  wetted  bibulous 
paper,  or  pieces  of  elder  pith  also  saturated  with  fluid,  are  to 
be  enclosed  with  the  object,  which  in  this  case  need  not  be 
covered  with  thin  glass  in  the  usual  manner.  It  is  con- 
ceivable also  that  this  apparatus  may  easily  be  converted 
into  a  gas  chamber,  by  fixing  two  small,  light  vulcanized 


OF   MICROSCOPIC   OBJECTS.  23 

tubes  into  that  which  embraces  the  glass  ring  and  the  end 
of  the  microscope  tube — one  for  the  entrance,  the  other  for 
the  exit  of  the  gas.  This  is  a  simpler  and  less  costly  plan 
than  that  devised  by  Strieker.  Frey  observes  that  it  is 
most  advantageous  to  use  immersion  lenses  and  the  moist 
chamber  with  the  hot  stage. 


21  PREPARATION   AND   MOUNTING 


CHAPTEE    II. 

APPARATUS. 

BEFORE  entering  into  the  subject  of  the  setting  of  Objects 
for  the  Microscope,  the  student  must  be  convinced  of  the 
necessity  of  cleanliness  in  everything  relating  to  the  use  of 
that  instrument.  la  no  branch  is  this  more  apparent  than 
in  the  preparation  of  objects ;  because  a  slide  which  would 
be  considered  perfectly  clean  when  viewed  in  the  ordinary 
way  is  seen  to  be  far  otherwise  when  magnified  some  hun- 
dreds of  diameters ;  those  constant  enemies,  the  floating 
particles  of  dust,  are  everywhere  present,  and  it  is  only 
by  unpleasant  experience  that  we  fully  learn  what  cleanli- 
ness is. 

An  object  which  is  to  be  viewed  under  the  microscope 
must,  of  course,  be  supported  in  some  way — this  is  now 
usually  done  by  placing  it  upon  a  glass  slide,  which  on 
account  of  its  transparency  has  a  great  advantage  over 
other  substances.  These  "slides"  are  almost  always  made 
of  one  size,  viz.,  three  inches  long  by  one  broad,  generally 
having  the  edges  ground  so  as  to  remove  all  danger  of 
scratching  or  cutting  any  object  with  which  they  may  come 
in  contact.  The  glass  must  be  very  good,  else  the  surface 
will  always  present  the  appearance  of  uncleanliness  and  dust. 
This  dusty  look  is  very  common  amongst  the  cheaper  kinds 
of  slides,  because  they  are  usually  made  of  "sheet"  glass  ; 
but  is  seldom  found  in  those  of  the  quality  known  amongst 
dealers  by  the  name  of  "patent  plate."  This  latter  is  more 
expensive  at  first,  but  in  the  end  there  is  little  difference  in 
the  cost,  as  so  many  of  the  cheaper  slides  cannot  be  used 
for  delicate  work  if  the  mounted  object  is  to  be  seen  in  per- 
fection. These  slides  vary  considerably  in  thickness  ;  care 


OF   MICROSCOPIC   OBJECTS.  25 

should,  therefore,  be  taken  to  sort  them,  so  that  the  more 
delicate  objects  with  which  the  higher  powers  are  to  be 
used  may  be  mounted  upon  the  thinnest,  as  the  light  em- 
ployed in  the  illumination  is  then  less  interfered  with.  To 
aid  the  microscopist  in  this  work,  a  metal  circle  may  be  pro- 
cured, having  a  number  of  different  sized  openings  on  the 
outer  edge,  by  which  glass  slides  can  be  measured.  These 
openings  are  numbered,  and  the  slides  may  be  separated 
according  to  these  numbers;  so  that  when  mounting  any 
object  there  will  be  no  need  of  a  long  search  for  that  glass 
which  is  best  suited  to  it. 

When  fresh  from  the  dealer's  hands,  these  slides  are 
generally  covered  with  dust,  &c.,  which  may  be  removed  by 
well  washing  in  clean  rain-water ;  but  if  the  impurity  is 
obstinate,  a  little  washing  eoda  may  be  added,  care  being 
taken,  however,  that  every  trace  of  this  is  removed  by  sub- 
sequent waters,  otherwise,  crystals  will  afterwards  form  upon 
the  surface.  Sometimes,  however,  a  certain  greasiness  is 
very  obstinate  upon  the  glass.  It  is  then  necessary  to  use 
a  little  liquor  potassae  with  a  small  piece  of  linen,  rubbing 
the  slide  with  some  pressure,  and  then  washing  as  before  to 
remove  all  remains.  A  clean  linen  cloth  should  be  used  to 
dry  the  slides,  after  which  they  may  be  laid  by  for  use. 
Immediately,  however,  before  being  used  for  the  reception  of 
objects  by  any  of  the  following  processes,  all  dust  must  be 
removed  by  rubbing  the  surface  with  clean  wash-leather  or 
a  piece  of  cambric,  and,  if  needful,  breathing  upon  it,  and 
then  using  the  leather  or  cambric  until  perfectly  dry.  Any 
small  particles  left  upon  the  surface  may  generally  be 
removed  by  blowing  gently  upon  it,  taking  care  to  allow  no 
damp  to  remain.  A  very  efficient  remedy,  also,  is  a  mixture 
of  equal  parts  of  sulphuric  ether  and  alcohol,  with  which 
the  glass  must  be  rubbed  by  the  aid  of  a  tuft  of  clean 
cotton-wool  until  no  stain  appears  after  breathing  upon  it. 
A  strong  infusion  of  nutgalls  may  be  used  in  the  same  way, 
and  is  preferred  by  many  to  all  other  applications ;  or,  a 
mixture  of  equal  parts  of  alcohol,  benzole,  and  liquor  sodae 


26  PREPAKATION  AND  MOUNTING 

may  be  employed,  which  thoroughly  and  speedily  cleanses 
glass  from  all  traces  of  grease  or  balsam. 

We  have  before  said  that  any  object  to  be  viewed  in  the 
microscope  must  have  its  support;  but  if  this  object  is  to 
be  preserved,  care  must  be  taken  that  it  is  defended  from 
dust  and  other  impurities.  For  this  pnrpose  it  is  necessary 
to  use  some  transparent  cover,  the  most  usual  at  one  time 
being  a  plate  of  mica,  on  account  of  its  thinness ;  this  sub- 
stance is  now,  however,  never  used,  thin  glass  being  substi- 
tuted, which  answers  admirably.  Sometimes  it  is  required 
to  "  take  up  "  as  little  space  as  possible,  owing  to  the  short- 
ness of  focus  of  the  object-glasses.  It  can  be  procured  of 
any  thickness,  from  one-fiftieth  to  one-two-hundred-and- 
fiftieth  of  an  inch.  On  account  of  its  want  of  strength,  and 
probable  defect  of  due  annealing,  it  is  difficult  to  cut,  as  it 
is  very  liable  to  "fly  "  from  the  point  of  the  diamond.  To 
overcome  this  tendency  as  much  as  possible,  it  must  be  laid 
upon  a  thicker  piece,  previously  made  wet  with  water,  which 
causes  the  thin  glass  to  adhere  more  firmly,  and  conse- 
quently to  bear  the  pressure  required  in  cutting  the  covers. 
The  process  of  cutting  being  so  difficult,  especially  with  the 
thinner  kinds,  little  or  nothing  is  gained  by  cutting  those 
which  can  be  got  from  the  dealers,  as  the  loss  and  breakage 
is  necessarily  greater  in  the  hands  of  an  amateur.  It  is 
convenient,  however,  to  have  on  hand  a  few  larger  pieces, 
from  which  unusual  sizes  may  be  cut  when  required. 

If  the  pieces  required  are  rectangular,  no  other  apparatus 
will  be  required  save  a  diamond  and  a  flat  rule ;  but  if 
circles  are  wanted,  a  machine  for  that  purpose  shouM  be 
used  (of  which  no  description  is  necessary  here).  There  are, 
however,  other  contrivances  which  answer  tolerably  well. 
One  method  is,  to  cut  out  from  a  thick  piece  of  cardboard  a 
circle  rather  larger  than  the  size  wanted.  Dr.  Carpenter 
recommends  metal  rings  with  a  piece  of  wire  soldered  on 
either  side ;  and  this,  perhaps,  is  the  best,  as  cardboard  is 
apt  to  become  rough  at  the  edge  when  much  used.  A  friend 
of  mine  uses  thin  brass  plates  with  circles  of  various  sizes 


OF   MICKOSCOPIC   OBJECTS.  27 

"  turned  "  through  them,  and  a  small  raised  handle  placed 
at  one  end.  The  diamond  must  be  passed  round  the  inner 
edge,  and  so  managed  a8  to  meet  again  in  the  same  line,  in 
order  that  the  circle  may  be  true,  after  which  it  may  be 
readily  disengaged.  The  sizes  usually  kept  in  stock  by  the 
dealers  are  one-half,  five-eighths,  and  three-quarters  inch 
diameter ;  but  other  sizes  may  be  had  to  order. 

For  the  information  of  the  beginner  it  may  be  mentioned 
here  that  the  price  of  the  circles  is  a  little  more  than  that 
of  the  squares ;  but  this  is  modified  in  some  degree  by  the 
circles  being  rather  lighter.  If  appearance,  however,  is 
cared  for  at  all,  the  circles  look  much  neater  upon  the  slides 
when  not  covered  with  the  ornamental  papers ;  but  if  these 
last  are  used  (as  will  shortly  be  described)  the  squares  are 
equally  serviceable. 

As  before  mentioned,  the  thin  glass  is  made  of  various 
thicknesses,  and  the  beginner  will  wish  to  know  which  to 
use.  For  objects  requiring  no  higher  power  than  the  one- 
inch  object-glass,  the  thicker  kinds  serve  well  enough ;  for 
the  half-inch  the  medium  thickness  will  be  required ;  while, 
for  higher  powers,  the  thinnest  covers  must  be  used.  The 
"  test-objects  "  for  the  highest  powers  require  to  be  brought 
so  near  to  the  object-glass  that  they  admit  of  the  very 
thinnest  covering  only,  and  are  usually  mounted  betwixt 
glasses  which  a  beginner  would  not  be  able  to  use  without 
frequent  breakage ;  bat  if  these  objects  were  mounttd  with 
the  common  covers,  they  would  be  really  worthless  with  the 
powers  which  they  require  to  show  them  satisfactorily. 

It  may  be  desirable  to  know  how  such  small  differences 
as  those  betwixt  the  various  thin  glass  covers  can  be 
measured.  For  this  purpose  there  are  two  or  three  sorts  of 
apparatus,  all,  however,  depending  upon  the  same  principle. 
The  description  of  one,  therefore,  will  be  sufficient.  Upon  a 
small  stand  is  a  short  metal  lever  (as  it  may  be  termed) 
which  returns  by  a  spring  to  one  certain  position,  where  it 
is  in  contact  with  a  fixed  piece  of  metal.  At  the  other  end 
this  lever  is  connected  with  a  "  finger,"  which  moves  round 


28  PREPARATION   AND   MOUNTING 

a  dial  like  that  of  a  watch,  whereupon  are  figures  at  fixed 
distances.  When  the  lever  ia  separated  from  the  metal 
which  is  stationary,  the  other  end  being  connected  with  the 
"  finger,"  of  the  dial,  that  "  finger  "  is  moved  in  proportion 
to  the  distance  of  the  separation.  The  thin  glass  is,  there- 
fore, thrust  betwixt  the  end  of  the  lever  and  fixed  metal,  and 
each  piece  is  measured  by  the  figures  on  the  dial  in  stated 
and  accurate  degrees.  This  kind  of  apparatus,  however,  is 
expensive,  and  when  not  at  our  command,  thin  glass  may 
be  placed  edgewise  in  the  stage  forceps,  and  measured  very 
accurately  with  the  micrometer,  or  by  the  calliper  eye- 
piece described  by  Dr.  Matthews  in  JSTo.  8,  for  October,  1869, 
of  the  Journal  of  the  Quekett  Microscopical  Club. 

Cleanliness  with  thin  glass  is,  perhaps,  more  necessary 
than  with  the  sides,  especially  when  covering  objects  which 
are  to  be  used  with  a  high  power;  but  it  is  far  more  difficult 
to  attain,  on  account  of  the  liability  to  breakage.  The 
usual  method  of  cleaning  these  covers  is  as  follows  : — Two 
discs  of  wood,  about  two  inches  in  diameter,  are  procured, 
one  side  of  each  being  perfectly  flat  and  covered  with  clean 
wash-leather.  To  the  other  side  of  these  a  small  knob  is 
firmly  fixed  as  a  handle,  or  where  practicable,  the  whole 
may  be  made  out  of  a  solid  piece.  In  cleaning  thin  glass, 
it  should  be  placed  betwixt  the  covered  sides  of  the  discs, 
and  may  then  be  safely  rubbed  with  a  sufficient  pressure, 
and  so  cleaned  on  both  sides  by  the  leather.  If,  however, 
the  glass  be  greasy,  as  is  sometimes  the  case,  it  must  be 
first  washed  with  a  strong  solution  of  potash,  infusion  of 
nutgalls,  or  any  of  the  commonly  used  grease-removing 
liquids ;  and  with  some  impurities  water,  with  the  addition 
of  a  few  drops  of  strong  acid,  will  be  found  very  useful,  but 
this  last  is  not  often  required. 

This  method  of  cleaning  thin  glass  should  always  be  used 
by  beginners ;  but  after  some  experience  the  hand  becomes 
so  sensitive  that  the  above  apparatus  is  often  dispensed 
with,  and  the  glasses,  however  thin,  may  be  safely  cleaned 
betwixt  the  fingers  and  thumb  with  a  cambric  handkerchief, 


OF    MICROSCOPIC   OBJECTS.  29 

having  first  slightly  damped  the  ends  of  the  fingers  employed 
to  obtain  firm  hold.  When  the  dirt  is  very  obstinate, 
breathing  npon  the  glass  greatly  facilitates  its  removal,  and 
the  sense  of  touch  becomes  so  delicate  that  the  breakage  is 
inconsiderable;  but  this  method  cannot  be  recommended  to 
novices,  as  nothing  but  time  spent  in  delicate  manipulation 
can  give  the  sensitiveness  required. 

It  has  been  before  mentioned  that  ordinary  glass  sides  arc 
sometimes  worthless,  especially  for  fine  objects,  from  having 
a  rough  surface,  which  presents  a  dusty  appearance  under 
the  microscope.  This  imperfection  exists  in  some  thin  glass 
also,  and  is  irremediable;  so  that  it  is  useless  to  attempt  to 
cleanse  it ;  nevertheless,  care  should  be  taken  not  to  mistake 
dirt  for  this  roughness,  lest  good  glass  be  laid  aside  for  a 
fault  which  does  not  really  belong  to  it. 

When  any  object  which  it  is  desired  to  mount  is  of  con- 
siderable thickness,  or  will  not  bear  pressure,  it  is  evident 
that  a  wall  must  be  raised  around  it  to  support  the  thin 
g'ass — this  is  usually  termed  a  "cell."  There  are  various 
descriptions  of  these,  according  to  the  class  of  objects  they 
are  required  to  protect ;  and  here  may  be  given  a  description 
of  those  which  are  most  generally  used  in  mounting  "  dry  " 
objects,  leaving  those  required  for  the  preservation  of  liquids 
until  we  come  to  the  consideration  of  that  mode  of  mounting. 
Many  have  used  the  following  slides.  Two  pieces  of  hard 
•wood  of  the  usual  size  (3  in.  by  1  in.),  not  exceeding  one- 
sixteenth  of  an  inch  in  thickness,  are  taken,  and  a  hole  is 
then  drilled  in  the  middle  of  one  of  these  of  the  size  required. 
The  two  pieces  are  then  united  by  glue  or  other  cement, 
and  left  under  pressure  until  thoroughly  dry,  when  the  cell 
is  fit  for  use.  Others  substitute  cardboard  for  the  lower 
piece  of  wood,  which  is  less  tedious,  and  is  strong  enough 
for  every  purpose.  This  class  of  "  cell "  is,  of  course,  fitted 
for  opaque  objects  only  where  no  light  is  required  from 
below  ;  and  as  almost  all  such  are  better  seen  when  on  a  dark 
background,  it  is  usual  to  fix  a  small  piece  of  black  paper 
at  the  bottom  of  the  cell  upon  which  to  place  them.  For 


30  PREPARATION  AND  MOUNTING 

very  small  objects  the  grain  which  all  such  paper  has 
when  magnified  detracts  a  little  from  the  merit  of  this 
background;  and  lately  I  have  used  a  small  piece  of  thin 
glass  covered  on  the  back  with  black  varnish,  and  placed  the 
object  upon  the  smooth  untouched  side ;  but  a  solution  of 
the  best  Egyptian  asphalt  in  benzole  of  moderate  thick- 
ness may  be  painted  on  with  this  further  advantage, 
that  in  mounting  such  opaque  objects  as  foraminifera,  &c., 
it  will  be  sufficient  to  arrange  them  in  the  positions  they 
are  to  occupy,  when  by  slightly  warming  the  slide  they 
will  adhere  to  the  asphalt. 

Another  method  of  making  these  cells  is  as  follows : — 
Two  punches,  similar  to  those  used  for  cutting  gun-wads, 
are  procured,  of  such  sizes  that  with  the  smaller  mav  be  cut 
out  the  centre  of  the  larger,  leaving  a  ring  whose  side  is  not 
less  than  an  one-eighth  of  an  incli  wide.  These  rings  may 
be  readily  made,  the  only  difficulty  being  to  keep  the  sides 
parallel ;  but  a  little  care  will  make  this  easy  enough.  For 
this  purpose  close-grained  cardboard  may  be  conveniently 
used.  It  must  have  a  well-glazed  surface,  else  the  varnish 
or  cement  used  in  affixing  the  thin  glass  cover  sinks  into  the 
substance,  and  the  adherence  is  very  imperfect.  When  this 
takes  place  it  is  easily  remedied  by  brushing  over  the  sur- 
face of  the  cardboard  a  strong  solution  of  gum  or  isin- 
glass ;  and  this  application,  perhaps,  closes  also  the  pores 
of  the  card,  and  so  serves  a  double  purpose.  But,  of 
course,  the  gum  must  be  perfectly  dried  before  the  ring  is 
used. 

For  cardboard,  gutta-percha  has  been  substituted,  but 
cannot  be  recommended,  as  it  always  become  brittle  after 
a  certain  time,  never  adheres  to  the  glass  with  the  required 
firmness,  and  its  shape  is  altered  when  worked  with  even  a 
little  heat.  Leather  is  often  used,  and  is  very  convenient ; 
it  should  be  chosen,  however,  of  a  close  texture,  and  free 
from  oil,  grease,  and  all  those  substances  which  are  laid 
upon  it  by  the  dressers. 

Rings  of  cardboard,  &c.,  have  been  rejected  by  persons  of 


OF   MICROSCOPIC   OBJECTS.  31 

great  experience,  because  they  are  of  such  a  nature  that 
dampness  can  penetrate  them.  This  fault  can  be  almost,  if 
not  totally,  removed  by  immersing  them  in  some  strong 
varnish,  such  as  the  asphalt  varnish  hereinafter  mentioned; 
but  they  must  be  left  long  enough  when  affixed  to  the  glass 
slide  to  become  perfectly  dry,  and  this  will  require  a  much 
longer  time  than  at  first  would  be  supposed. 

There  has,  however,  been  lately  brought  out  what  is 
termed  the  ivory  cell.  This  is  a  ring  of  ivory-like  substance, 
which  may  be  easily  and  firmly  fixed  to  the  glass  slide  by 
any  of  the  commonly  used  cements,  and  so  forms  a  beautiful 
cell  for  any  dry  objects.  They  are  made  of  different  sizes, 
and  are  not  expensive.  Flat  rings  of  brass  turned  down  to  the 
sizes  of  the  circular  discs  of  covering  glass  and  of  varying 
thickness  are  very  neat  and  useful  for  mounting  opaque 
objects :  they  can  also  be  obtained  in  tin  and  zinc. 

Some  of  our  best  microscopic  men  have  stated  that  they 
have  been  frequently  disappointed  by  an  accumulation  of 
encrusted  matter  upon  the  inner  surface  of  thin  glass  used 
to  cover  the  cell  enclosing  any  dry  object,  and  therefore  use 
a  shallow  pillbox,  made  expressly  for  this  purpose,  which 
must  be  strongly  cemented  to  the  slide.  For  examination 
the  lid  must  be  removed,  whilst  it  must  be  closed  to  protect 
the  object  from  dust  when  laid  aside.  Another  worker  of 
experience  recommends  a  cell  in  a  mahogany  slide,  over 
which,  b}'  aid  of  a  stud  as  on  a  pivot,  a  bone  disk  can  be 
turned :  this  is  termed,  "  Piper's  Revolving  Cover  Slide," 
and  can  be  procured  at  the  opticians'. 

Sometimes  slides  are  used  which  are  made  by  taking  a 
thin  slip  of  wood  of  the  usual  size  (3  in.  by  1  in.),  in  the 
centre  of  which  is  cut  a  circular  hole  large  enough  to 
receive  the  object.  A  piece  of  thin  glass  is  fixed  underneath 
the  slide  forming  a  cell  for  the  object,  which  may  then  be 
covered  and  finished  like  an  ordinary  slide.  This  has  the 
advantage  of  serving  for  transparent  objects  for  which  the 
before-mentioned  wooden  slides  are  unsuitable.  A  slight 
modification  of  this  plan  is  often  used  where  the  thickness 


32  PREPARATION   AND   MOUNTING 

of  the  objects  is  inconsiderable,  especially  with  some  of  the 
Diatomaceas,  often  termed  "  test-objects."  The  wooden 
slide  is  cut  with  the  central  opening  as  above,  and  two 
pieces  of  thin  glabs  are  laid  upon  it,  betwixt  which  the 
diatoms  or  other  objects  are  placed,  and  kept  in  their  proper 
position  by  a  paper  cover.  This  arrangement  is  a  good 
one,  insomuch  as  the  very  small  portion  of  glass  through 
which  the  light  passes  on  its  way  to  the  microscope  from 
the  reflector  causes  the  refraction  or  interference  to  be 
reduced  to  the  lowest  point. 

A  novice  would  naturally  think  the  appearance  of  some 
of  the  slides  above  mentioned  very  slovenly  and  unfinished; 
but  they  are  often  covered  with  ornamental  papers,  which 
may  be  procured  at  almost  every  optician's,  at  a  cost 
little  more  than  nominal,  and  of  innumerable  patterns  and 
colours.  How  to  use  these  will  be  described  in  another 
place. 

It  is  very  probable  that  a  beginner  would  ask  his  friend 
what  kind  of  slides  he  would  advise  him  to  use.  Almost 
all  those  made  of  wood  are  liable  to  warp  more  or  less,  even 
when  the  two  pieces  are  separate  or  of  different  kinds ;  those 
of  cardboard  and  wood  are  generally  free  from  this  fault, 
yet  the  slides,  being  opaque,  prevent  the  employment  of 
the  Lieberkuhn.  To  some  extent  glass  sides,  when  covered 
with  ornamental  papers,  are  liable  to  the  same  objection, 
as  the  light  is  partly  hindered.  And  sometimes  dampness 
from  the  paste,  or  other  substance  used  to  affix  the  papers, 
penetrates  to  the  object,  and  so  spoils  it,  though  this  may 
be  rendered  less  frequent  by  first  attaching  the  thin  glass  to 
the  slide  by  some  harder  cement.  Much  time,  however, 
is  taken  up  by  the  labour  of  covering  the  slides,  which  is  a 
matter  of  consideration  with  some.  Certainly  the  cost  of 
the  glass  slides  was  formerly  great;  but  now  they  are 
reasonable  enough  in  this  respect,  so  that  this  objection  is 
removed.  It  is,  therefore,  well  to  use  glass  slides,  except 
where  the  thin  glasses  are  employed  for  tests,  &c.,  as  above. 
When  the  thin  glass  circles  are  placed  upon  the  slides,  and 


OF   MICBOSCOPIC   OBJECTS.  33 

the  edge  is  varnished  with  black  or  coloured  rings,  the 
appearance  of  finish  is  perfect.  The  trouble  is  much  less 
than  with  most  of  the  other  methods,  and  the  illumination 
of  the  object  very  slightly  impaired. 

To  varnish  the  edges  of  these  covers,  make  circles  of  any 
liquid  upon  the  glass  slide,  and  perform  any  other  circular 
work  mentioned  hereafter,  the  little  instrument  known  as 
"  Shadbolt's  turntable  "  is  almost  indispensable.  It  is  made 
as  follows : — At  one  end  of  a  small  piece  of  hard  wood  is 
fixed  an  iron  pivot  about  one-eighth  inch  thick,  projecting 
half  an  inch  from  the  wood,  which  serves  as  a  centre  upon 
which  a  round  brass  table  three  inches  in  diameter  revolves. 
On  the  surface  of  this  are  two  springs,  about  one  and  a  half- 
inch  apart,  under  which  the  slide  is  forced  and  so  kept  in 
position,  whilst  the  central  part  is  left  open  to  be  worked 
upon.  The  centre  is  marked,  and  two  circles  half  an  inch 
and  one  inch  in  diameter  are  usually  deeply  engraved  upon 
the  table  to  serve  as  guides  in  placing  the  slide,  that  the 
ring  may  be  drawn  in  the  right  position.  When  the  slide 
is  placed  upon  the  table  underneath  the  springs,  a  camel- 
hair  pencil  is  filled  with  the  varnish,  or  other  medium  used, 
and  applied  to  the  surface  of  the  glass ;  the  table  is  then 
made  to  revolve,  and  a  circle  is  consequently  produced,  the 
diameter  of  which  it  is  easy  to  regulate.  Mr.  Hislop  places 
two  equidistant  pins  at  opposite  sides  of  the  centre  of 
the  revolving  plate,  against  which  the  opposing  edges  of 
the  slip  are  made  to  bear,  so  that  the  instrument  is  self- 
centering.  The  springs  are  turned  in  contrary  directions  and 
are  screwed  on  the  pins,  or  the  screws  are  made  into  the 
pins  against  which  the  sides  of  the  slide  bear. 

The  form  of  this  "  turntable  "  has  been  modified  by  many 
manipulators  to  suit  their  several  wants.  Almost  all  slides 
used  are  of  nearly  the  same  size — 3  in.  by  1  in. ;  and  therefore 
the  centres  of  all  are  equidistant  from  the  edge.  On  this 
account  one  of  my  friends  has  a  thin  brass  bar  screwed  upon 
the  side  of  his  turntable  in  such  a  position  that  the  centres 
of  the  slides  and  table  always  coincide.  The  rings  of  varnish 


34  PREPARATION   AND   MOUNTING 

upon  the  slides  and  thin  glass  upon  the  cell  are  thus  kept 
uniform.  Dr.  Matthews,  a  gentleman  of  no  little  experience, 
has  given  us  an  improvement  as  follows  : — Take  two  "jaws  " 
of  the  average  thickness  of  a  glass  slide,  f  inch  wide,  2J 
long.  Each  of  these  is  pivoted  on  the  face  of  the  turntable 
by  a  screw  through  its  centre,  each  screw  being  placed 
exactly  equidistant  from  the  centre  of  the  turntable,  so  that 
the  jaws  are  separated  by  a  space  as  wide  as  an  average 
slide;  i.e.  a  full  inch.  Outside  of  that  space,  on  one  side  of 
the  centre  of  one  of  the  jaws,  is  a  wedge  fixed  by  a  screw  in 
such  a  way  as  to  be  capable  of  motion  in  the  direction  of 
its  length  by  a  slotted  hole.  This  is  all  the  machinery. 
AB  and  CD  are  the  two  jaws,  E  is  the  wedge.  On  placing 
a  slip  between  the  jaws  they  probably  at  first  do  not  touch 
it.  If  the  wedge  be  then  pushed  so  as  to  approximate  B  to 
C,  the  jaws  move  on  their  centres,  so  that,  however  far  B 
may  be  pushed  towards  (and  moving)  C,  the  other  end  of 
C — i.e,  D — is  moved  exactly  as  much  in  the  opposite  direc- 
tion vintil  they  approach  near  enough  to  grasp  the  slide  by 
its  edges.  The  length  of  the  wedge  must,  of  course,  be  such 
as  to  provide  for  about  |-  inch  variation  in  the  width  of 
elides.  It  will  readily  be  seen  that  the  slip  may  be  pushed 
in  either  direction  excentrically  lengthwise,  so  as  to  allow  of 
the  formation  of  any  number  of  cells,  all  of  which  must 
needs  be  central  as  regards  their  width,  if  the  instrument 
has  been  accurately  made,  which  is  a  very  easy  matter.  I 
have  added  also  a  rest  for  the  hand,  F,  which  may  be  turned 
aside  on  a  centre  at  will,  and  which  I  have  found  to  be  a 
great  convenience. 


OF   MICROSCOPIC   OBJECTS.  35 


6 


DR.  MATTHEWS'  TURNTABLE, 
D  2 


36 


PREPARATION   AND   MOUNTING 


Mr.  Spencer  slightly  modifies  the  above,  using  wood 
jaws  and  wedge,  which  the  following  engraving  will  best 
explain. 


DR.  MATTHEWS'  TURNTABLE,  TWO-THIRD  SIZE. 


Many  objects  for  the  microscope  may  be  seriously  injured 
by  allowing  the  fingers  to  touch  them — many  more  are  so 
minute  that  they  cannot  be  removed  in  this  way  at  all,  and 
often  it  is  necessary  to  take  from  a  mass  of  small  grains,  as 
in  sand,  some  particular  particle.  To  accomplish  this,  there 
are  two  or  three  contrivances  recommended :  one  by  means 
of  split  bristles,  many  of  which  will  readily  be  found  in 
any  shaving-brush  when  it  has  been  well  used.  The  bristles 
when  pressed  upon  any  hard  surface,  open,  and  when  the 
pressure  is  removed  close  again  with  a  spring ;  but  the  use 
of  these  is  limited.  Camel-hair  pencils  are  of  great  service 
for  this,  and  many  other  purposes,  to  the  microscopist. 
In  very  fine  work  they  are  sometimes  required  so  small  that 
all  the  hairs,  with  the  exception  of  one  or  two  finer  pointed 


OF   MICROSCOPIC   OBJECTS.  37 

ones,  are  removed.  A  few  of  various  sizes  should  always  be 
kept  on  hand. 

Equally  necessary  are  fine-pointed  needles.  They  are 
very  readily  put  up  for  use  by  thrusting  the  eye  end  into 
a  common  penholder,  so  as  to  be  firm.  The  points  may  be 
readily  renewed,  when  injured,  on  a  common  whetstone ; 
and  when  out  of  use  they  may  be  protected  by  being  thrust 
into  a  piece  of  cork. 

In  laying  out  animal  tissues  that  have  been  stained  by 
nitrate  of  silver  or  chloride  of  gold,  it  is  advisable  to  employ 
i  small  rod  of  glass  drawn  out  to  a  point,  as  the  use  of  a 
metallic  point  causes  a  deposit  of  gold  or  silver  at  the  place 
of  contact,  which  disfigures  the  preparation. 

Knives  of  various  kinds  are  required  in  some  branches 
of  microscopic  work ;  but  these  will  be  described  where 
iissection,  &c.,  is  treated  at  some  length,  as  also  various 
forms  of  scissors.  In  the  most  simple  objects,  however, 
scissors  of  the  usual  kind  are  necessary.  Two  or  three 
sizes  should  always  be  kept  at  hand,  sharp  and  in  good 
order. 

A  set  of  glass  tubes,  kept  in  a  case  of  some  sort  to 
prevent  breakage,  should  form  part  of  our  fittings,  and 
be  always  cleaned  immediately  after  use.  These  are 
generally  from  six  to  ten  inches  long,  and  from  one-eighth 
to  a  quarter  of  an  inch  in  diameter.  One  of  these  should 
be  straight  and  equal  in  width  at  both  ends  ;  one  should  be 
drawn  out  gradually  to  a  fine  point ;  another  should  be 
pointed  as  the  last,  but  slightly  curved  at  the  compressed 
end,  in  order  to  reach  points  otherwise  unattainable.  It  is 
well  to  have  these  tubes  of  various  widths  at  the  points,  as 
in  some  waters  the  finer  would  be  inevitably  stopped.  For 
other  purposes  the  fine  ones  are  very  useful,  especially  in 
the  transfer  of  preservative  liquids  which  will  come  under 
notice  in  another  chapter. 

Forceps  are  required  in  almost  all  microscopic  manipu- 
lations, and  consequently  are  scarcely  ever  omitted  from  the 
microscopic  box,  even  the  most  meagrely  furnished  ;  but  of 


38  PREPARATION   AND  MOUNTING 

these  there  are  various  modifications,  which  for  certain 
purposes  are  more  convenient  than  the  usual  form.  The 
ordinary  metal  ones  are  employed  for  taking  up  small 
objects,  thin  glass,  &c. ;  but  when  slides  are  to  be  held  over 
a  lamp,  or  in  any  position  where  the  fingers  cannot  con- 
veniently be  used,  a  different  instrument  must  be  found. 
Of  these  there  are  many  kinds ;  but  Mr.  Page's  wooden 
forceps  serve  the  purpose  very  well.  Two  pieces  of  elastic 
wood  are  strongly  bound  together  at  one  end,  so  that  they 
may  be  easily  opened  at  the  other,  closing  again  by  their 
own  elasticity.  Through  the  first  of  these  pieces  is  loosely 
passed  a  brass  stud,  resembling  a  small  screw,  and  fastened 
in  the  second,  and  through  the  second  a  similar  stud  is 
taken  and  fixed  in  the  first — so  that  on  pressure  of  the  studs 
the  two  strips  of  wood  are  opened  to  admit  a  slide  or  other 
object  required  to  be  held  in  position.  The  wood  strips  are 
generally  used  three  or  four  inches  long,  one  inch  wide,  and 
about  one-eighth  inch  thick. 

Again,  some  objects  when  placed  upon  the  glass  slide  arc 
of  such  an  elastic  nature  that  no  cement  will  secure  the 
thin  glass  covering  until  it  becomes  hard.  This  difficulty 
may  be  overcome  by  various  methods.  The  following  are 
as  good  and  simple  as  any.  Take  two  pieces  of  wood  about 
two  inches  long,  three-quarters  wide,  and  one-quarter  thick  ; 
and  a  small  rounded  piece  one  inch  long,  and  one-quarter  in 
diameter;  place  this  latter  betwixt  the  two  larger  pieces. 
Over  one  end  of  the  two  combined  pass  an  india-rubber 
band.  This  will  give  a  continual  pressure,  and  may  be 
opened  by  bringing  the  two  pieces  together  at  the  other 
end ;  the  pressure  may  be  readily  made  uniform  by  paring 
the  points  at  the  inner  sides,  and  may  be  regulated  by  the 
strength  of  the  india-rubber  band.  These  bands  may  be 
made  cheaply,  and  of  any  power,  by  procuring  a  piece  of 
india-rubber  tubing  of  the  width  required,  and  cutting  off 
certain  breadths.  Another  very  simple  method  of  getting 
this  pressure  is  mentioned  in  the  "Micrographic  Dictionary." 
Two  pieces  of  whalebone  of  the  length  required  are  tied 


OF   MICROSCOPIC   OBJECTS.  39 

together  firmly  at  each  end.  It  is  evident  that  any  object 
placed  betwixt  them  will  be  subject  to  continual  pressure. 
The  power  of  this  may  be  regulated  by  the  thickness  and 
length  of  the  whalebone.  This  simple  contrivance  is  very 
useful. 

Almost  every  scientific  man,  however,  has  his  own  model, 
and  it  may  be  as  well  to  examine  one  or  two  of  them.  Mr. 
Goode  uses  the  following :  A,  a  piece  of  wood  8  in.  long 
and  f  in.  thick.  B,  a  spring,  made  with  thin  iron  wire. 
The  end  of  the  spring  is  driven  into  the  table,  as  at  C.  A 
piece  of  |-in.  iron  wire  is  then  run  through  the  springs,  which 
forms  an  axis  to  work  upon,  and  also  keeps  them  in  their 
places.  He  inserts  a  pin  at  the  side  of  the  spring,  so  that 
it  will  fall  on  a  given  spot,  and  not  rub  the  cover  from  side 
to  side.  The  springs  are  made  by  binding  the  thin  wire 
round  the  |-in.  rod  about  four  or  five  times. 


40 


PREPARATION   AND   MOUNTING 


•WIRE    CLIP. 


OF   MICROSCOPIC   OBJECTS.  41 

Mr.  J.  B.  Spencer's  model  is  made  thus : — It  is  formed 
of  thin  sheet  steel  (obtainable  at  any  instrument  maker's),  and 
cut  out  in  one  piece,  of  the  form  above,  with  a  stout  pair  of 
scissors,  and  then  bent  the  required  shape  with  a  pair  of 
pliers.  "When  used,  the  fore  and  middle  fingers  are  applied 
on  the  under  side,  and  the  thumb  on  the  spring.  If  great 
pressure  is  required,  two  clips  may  be  used, — one  at  each 
end  of  the  slide, — and  for  any  delicate  work  the  width  of 
the  steel  can  be  reduced. 


STEEL    CLIP. 

The  American  wooden  spring  clips  are  occasionally  very 
useful,  and  wire  clips  of  the  kind  described  by  Dr.  Carpenter 
are  now  commonly  sold  and  are  indispensable. 

Common  watch-glasses  should  always  be  kept  at  hand. 
They  are  certainly  the  cheapest,  and  their  transparency 
makes  them  very  convenient  reservoirs  in  which  objects  may 


42  PREPARATION   AND   MOUNTING 

be  steeped  in  any  liquid ;  and  the  use  of  them  saves  much 
trouble  in  examining  cursorily  under  the  microscope,  whether 
the  air-bubbles  are  expelled  from  insects,  &c.  &c.  They  are 
readily  cleaned,  and  serve  very  well  as  covers,  when  turned 
upside  down,  to  protect  objects  from  dust.  For  this  latter 
purpose  Dr.  Carpenter  recommends  the  use  of  a  number  of 
bell-glasses,  especially  when  one  object  must  be  left  for  a 
time  (which  often  happens)  in  order  that  another  may  be 
proceeded  with.  Wine-glasses,  when  the  legs  are  broken, 
may  thus  be  rendered  very  useful. 

As  heat  is  necessary  in  mounting  many  obejects,  a  lamp 
will  be  required.  Where  gas  is  used,  the  small  lamp  known 
as  "Bunsen's"  is  the  most  convenient  and  inexpensive.  It 
gives  great  heat,  is  free  from  smoke,  and  is  readily  affixed 
to  the  common  gas-burner  by  a  few  feet  of  india-rubber 
tubing.  The  light  from  these  lamps  is  small,  but  this  is 
little  or  no  drawback  to  their  use.  Where  gas  is  not  avail- 
•  able,  the  common  spirit-lamps  may  be  used,  as  they  are  very 
clean  and  answer  every  purpose. 

In  applying  the  required  heat  to  the  slides,  covers,  &c.,  it 
is  necessary  in  all  cases  to  ensure  uniformity,  otherwise 
there  is  danger  of  the  glass  being  broken.  For  this  purpose 
a  brass  plate  at  least  three  inches  wide,  somewhat  longer, 
and  one-eighth  of  an  inch  thick  must  be  pi'ocured.  It 
should  then  be  affixed  to  a  stand,  so  that  it  may  be  readily 
moved  higher  or  lower,  in  order  that  the  distance  from  the 
lamp  may  be  changed  at  will,  and  thus  the  degree  of  heat 
more  easily  regulated.  This  has  also  the  advantage  of 
enabling  the  operator  to  allow  his  slides,  &c.,  to  cool  more 
gradually,  which,  in  some  cases,  is  absolutely  necessary, — 
as  in  fusing  some  of  the  salts,  &c. 

In  order  to  get  rid  of  air -bubbles,  which  are  frequently 
disagreeable  enemies  to  the  mounter  of  objects,  an  air-pump 
is  often  very  useful.  This  is  made  by  covering  a  circular 
plate  of  metal  with  a  bell-glass,  both  of  which  are  ground  so 
finely  at  the  edges  that  greasing  the  place  of  contact  renders 
it  air-tight.  The  pump  is  then  joined  to  the  metal  plate 


OF   MICROSCOPIC   OBJECTS.  43 

underneath,  and  worked  with  a  small  handle  like  a  common 
syringe.  By  turning  a  small  milled  head  the  air  may  be 
allowed  to  re-enter  when  it  is  required  to  remove  the  bell- 
glass  and  examine  or  perform  any  operation  upon  the  object. 
The  mode  of  using  this  instrument  will  be  described  here- 
after, but  it  may  be  here  stated  that  substitutes  have  been 
devised  for  this  useful  apparatus ;  but  as  it  is  now  to  be 
obtained  at  a  low  cost,  it  is  hardly  worth  while  to  consider 
them.  Much  time  is,  in  many  instances,  certainly  saved  by 
its  use,  as  a  very  long  immersion  in  the  liquids  would  be 
required  to  expel  the  bubbles,  where  the  air-pump  would 
remove  them  in  an  hour. 

The  next  thing  to  be  considered  is  what  may  be  termed 
CEMENTS,  some  of  which  are  necessary  in  every  method  of 
mounting  objects  for  the  microscope.  Of  these  will  be  given 
the  composition  where  it  is  probable  the  young  student  can 
use  it ;  but  many  of  them  are  so  universally  kept  as  to  be 
obtainable  almost  anywhere ;  and  when  small  quantities 
only  are  required,  economy  suffers  more  from  home  manu- 
facture than  from  paying  the  maker's  profit. 

Amongst  these,  CANADA  BALSAM  may,  perhaps,  be  termed 
the  most  necessary,  as  it  is  generally  used  for  the  preserva- 
tion of  many  transparent  objects.  It  is  a  thick  liquid  resin 
of  a  light  amber-colour,  which  on  exposure  to  the  atmosphere 
becomes  dry  and  hard  even  to  brittleness.  For  this  reason 
it  is  seldom  used  as  a  cement  alone  where  the  surface  of 
contact  is  small,  as  it  would  be  apt  to  be  displaced  by  any 
sudden  shock,  especially  when  old.  In  the  ordinary  method 
of  using,  however,  it  serves  the  double  purpose  of  preserving 
the  object  and  fixing  the  thin  glass  cover ;  whilst  the  com- 
paratively large  space  upon  which  it  lies  lessens  the  risk  of 
displacement.  By  keeping,  this  substance  becomes  thicker ; 
but  a  very  little  warmth  will  render  it  liquid  enough  to  use, 
even  when  to  some  extent  this  change  has  taken  place. 
When  heated,  however,  for  some  time  and  allowed  to  cool,  it 
becomes  hardened  to  any  degree,  which  may  b'e  readily 
regulated  by  the  length  of  time  it  has  been  exposed,  and 


44  PREPARATION   AND   MOUNTING 

the  amount  of  heat  to  which  it  haa  been  subjected.  On 
account  of  this  property  it  is  often  used  with  chloroform  : 
the  balsam  is  exposed  to  heat  until,  on  cooling,  it  assumes 
a  glassy  appearance.  This  will  be  most  readily  done  by 
baking  it  in  what  we  should  call  a  "  cool  oven."  The  time 
required  will  most  likely  be  20  or  30  hours.  Care  must  be 
taken  that  the  heat  is  not  too  great,  else  the  balsam  will  be 
discoloured.  It  must  then  be  dissolved  in  pure  chloroform 
or  benzole  (the  latter  is  preferable)  until  it  becomes  of  the 
consistence  of  thick  varnish.  This  liquid  is  very  convenient 
in  some  cases,  as  air-bubbles  are  much  more  easily  dispelled 
than  when  undiluted  Canada  balsam  is  used.  It  also  dries 
readily,  as  the  chloroform  evaporates  very  quickly,  for  which 
reason  it  must  be  preserved  in  a  closely-stoppered  bottle. 
It  has  been  said  that  this  mixture  becomes  cloudy  with  long 
keeping,  but  I  have  not  found  it  so  in  any  cases  where  I 
have  used  it.  Cloudiness  is  most  frequently,  if  not  always, 
caused  by  dampness  in  the  object,  as  mentioned  in  Chapter 
IV.  Should  it,  however,  become  so,  a  little  heat  will  gene- 
rally dispel  the  opacity.  The  ordinary  balsam,  if  exposed 
much  to  the  air  whilst  being  used,  becomes  thicker,  as  haa 
been  already  stated.  It  may  be  reduced  to  the  required 
consistency  with  common  turpentine ;  but  I  have  often  found 
this  in  some  degree  injurious  to  the  transparency  of  the 
balsam,  and  the  amalgamation  of  the  two  by  no  means 
perfect.  (See  also  Chapter  IV.)  Its  cheapness  renders  it 
no  extravagance  to  use  it  always  undiluted ;  and  when  pre- 
served in  a  bottle  with  a  hollow  cover  fitting  tightly  around 
the  neck,  both  surfaces  being  finely  ground,  it  remains  fit 
for  use  much  longer  than  in  the  ordinary  jar.  Canada  bal- 
sam may  now  be  procured  in  collapsible  tin  tubes,  like  those 
used  by  artists  ;  and  its  manipulation  is  thus  rendered  much 
more  easy,  cleanly,  and  convenient,  as  well  as  economical. 
Chloroform  is,  however,  frequently  used  for  dilution,  and  is 
perhaps  the  safest  solvent  we  can  employ. 

DAMMAR  VARNISH. — Some  complain  that  this  varnish  is 
not  easily  procurable  in  a  pure  transparent  state.  It  is 
often  used  by  our  American  friends  in  mounting  diatoms 


01    MICROSCOPIC   OBJECTS.  45 

and  other  fine  work.  It  is  very  liquid,  and  is  thought  by 
some  to  be  more  easily  worked  than  Canada  balsam. 
Dammar  may  be  easily  dissolved  in  benzole  to  any  extent. 
The  lumps  should  previously  be  scraped  until  they  are  freed 
from  dust  and  other  impurities,  and  then  roughly  crushed. 

ASPHALTUM. — This  substance  is  dissolved  in  linseed  oil, 
turpentine,  or  naphtha,  and  is  often  termed  "  Brunswick 
black."  It  is  easily  worked,  but  is  not  generally  deemed  a 
trustworthy  cement,  as  after  a  time  it  is  readily  loosened 
from  its  ground.  It  is,  however,  very  useful  for  some  pur- 
poses (such  as  "  finishing  "  the  slides),  as  it  dries  quickly. 
I  shall,  however,  mention  a  modification  of  this  cement  a 
little  farther  on. 

MARINE  GLUE. — ISTo  cement  is  more  useful  or  trustworthy 
for  certain  purposes  than  this.  It  is  made  in  various  pro- 
portions ;  but  one  really  good  mixture  is — equal  parts  of 
india-rubber  and  gum  shellac:  these  are  dissolved  in  mineral 
naphtha  with  heat.  It  is,  however,  much  better  to  get  it 
from  the  opticians  or  others  who  keep  it.  It  requires  heat 
in  the  application,  as  will  be  explained  in  Chapter  V. ;  but 
is  soluble  in  few,  if  any  of  the  liquids  used  by  the  microscopist, 
and  for  that  reason  is  serviceable  in  the  manufacture  of 
cells,  &c.  Where  two  pieces  of  glass  are  to  be  firmly 
cemented  together,  it  is  almost  always  employed ;  and  in  all 
glass  troughs,  plates  with  ledges,  &c.,  the  beginner  may  find 
examples  of  its  use. 

GOLD  SIZE.— This  substance  may  always  be  procured  at 
any  colourman's  shop.  The  process  of  its  preparation  is 
long  and  tedious.  It  is  therefore  not  necessary  to  describe 
it  here.  Dr.  Carpenter  says  that  it  is  very  durable,  and 
may  be  used  with  almost  any  preservative  liquids,  as  it  is 
acted  upon  by  very  few  of  them,  turpentine  being  its  only 
true  solvent.  If  too  thin,  it  may  be  exposed  for  awhile  to 
the  open  air,  which  by  evaporation  gradually  thickens  it. 
Care  must  be  taken,  however,  not  to  render  it  too  thick,  as 
it  will  then  be  useless.  A  small  quantity  should  be  kept  on 
hand,  as  it  is  much  more  adhesive  when  old. 

GUM   DAMMAR  CEMENT. — An  excellent  cement  may  be 


46  PREPARATION   AND   MOUNTING 

made  by  dissolving  gum  dammar  in  benzole,  and  adding 
about  one-third  of  gold  size  :  it  dries  very  readily,  and  is 
especially  useful  when  mounting  objects  in  fluid,  taking  care 
that  no  moisture  extends  beyond  the  covering  glass,  which 
would  prevent  the  complete  adhesion  of  the  cement.  In 
those  cases  where  glycerine  is  employed  as  the  mounting 
medium,  a  ring  of  liquid  glue  put  round  the  cover  first,  and 
•when  that  is  dry,  a  second  coat  of  gum  dammar  will  keep 
the  cover  very  secure,  and  no  leakage  take  place. 

LIQUID  GLUE  is  another  of  these  cements,  which  is  made 
by  dissolving  gum  shellac  in  naphtha  in  such  quantity  that 
it  may  be  of  the  required  consistency.  This  cement  appears 
to  me  almost  worthless  in  ordinary  work,  as  its  adherence 
can  never  be  relied  upon ;  but  it  is  so  often  used  and  recom- 
mended that  an  enumeration  of  cements  might  be  deemed 
incomplete  without  it.  Even  when  employed  simply  for 
varnishing  the  outside  of  the  glass  covers,  for  appearance's 
sake  alone,  it  invariably  chips.  Where,  however,  oil  is  used 
as  a  preservative  liquid,  it  serves  very  well  to  attach  the 
thin  glass  ;  but  when  this  is  accomplished,  another  varnish 
less  liable  to  chip  must  always  be  laid  upon  it.  (See 
Chapter  Y.)  Yet  it  makes  excellent  cells. 

BLACK  JAPAN. — This  is  prepared  from  oil  of  turpentine, 
linseed  oil,  amber,  gum  anime,  and  asphalt.  It  is  trouble- 
some to  make,  and  therefore  it  is  much  better  to  procure  it 
at  the  shops.  It  is  a  really  good  cement,  and  serves  very 
well  to  make  shallow  cells  for  liquids,  as  will  be  described  in 
Chapter  IV.  The  finished  cell  should  be  exposed  for  a 
short  time  to  the  heat  of  what  is  usually  termed  a  "  cool 
oven."  This  renders  it  very  durable,  and  many  very  careful 
manipulators  use  it  for  their  preparations. 

ELECTRICAL  CEMENT. — This  will  be  found  very  good  for 
some  purposes  hereinafter  described.  To  make  it,  melt 
together — 

5  parts  of  resin. 

1         „       beeswax. 

1  red  ochre. 


OF   MICROSCOPIC   OBJECTS.  47 

It  must  be  used  whilst  hot,  and  as  long  as  it  retains  even 
slight  warmth  can  be  readily  moulded  into  any  form.  It  is 
often  employed  in  making  shallow  cells  for  liquids,  as  before 
mentioned. 

GUM-WATER  is  an  article  which  nobody  should  ever  be 
without;  but  labels,  or  indeed  any  substance,  affixed  to 
glass  with  common  gum,  are  so  liable  to  leave  it  spon- 
taneously, especially  when  kept  very  dry,  that  I  have  lately 
added  five  or  six  drops  of  glycerine  to  an  ounce  of  the  gum 
solution.  This  addition  has  rendered  it  very  trustworthy 
even  on  glass,  and  now  I  never  use  it  without.  Ten  grains 
of  moist  sugar  to  each  ounce  of  gum  solution  will  also 
answer  equally  well.  This  solution  cannot  be  kept  long 
without  undergoing  fei'mentation,  to  prevent  which  the 
addition  of  a  small  quantity  of  any  essential  oil  (as  oil  of 
cloves,  &c.),  or  one-fourth  of  its  volume  of  alcohol,  may  be 
made,  which  will  not  interfere  in  any  way  with  its  use. 

There  is  what  is  sometimes  termed  an  extra  adhesive 
Turn-water,  which  is  made  with  the  addition  of  isinglass, 
Lhus : — Dissolve  two  drachms  of  isinglass  in  four  ounces  of 
distilled  vinegar;  add  as  much  gum  arabic  as  will  give  it 
the  required  consistency.  This  will  keep  very  well,  but  is 
apt  to  become  thinner,  when  a  little  more  gum  may  be 
added. 

I  may  here  mention  that  Messrs.  Marion  have  lately 
brought  out  a  cement  for  the  purpose  of  mounting  photo- 
graphs, which  is  very  adhesive,  even  to  glass.  I  find  it 
useful  in  all  cases  where  certainty  is  requisite ;  as  gummed 
paper  is  liable  in  a  dry  place  to  curl  from  the  slides,  as 
before  mentioned. 

All  these,  except  one  or  two,  are  liquid,  and  must  be  kept 
in  stoppered  bottles,  or,  at  least,  as  free  from  the  action  of 
the  air  as  possible. 

When  any  two  substances  are  to  be  united  firmly,  I  have 
termed  the  medium  employed  "  a  cement ;"  but  often  the 
appearance  of  the  elides  is  thought  to  be  improved  by 
drawing  a  coloured  f'.r™  upon  them,  extending  parti}' on  the 


48  PREPARATION   AND  MOUNTING 

cover  and  partly  on  the  slide,  hiding  the  junction  of  the  two. 
The  medium  used  in  these  cases  I  term  A  VARNISH,  and 
hereinafter  mention  one  or  two.  Of  course,  the  tenacity  is 
not  required  to  be  so  perfect  as  in  the  cements. 

SEALING-WAX  VARNISH  is  prepared  by  coarsely  powdering 
sealing-wax,  and  adding  spirits  of  wine ;  it  is  then  digested 
at  a  gentle  \heat  to  the  required  thickness.  This  is  very 
frequently  used  to  finish  the  slides,  as  before  mentioned, 
and  can  easily  be  made  of  any  colour  by  employing  different 
kinds  of  sealing-wax;  but  is  very  liable  to  chip  and 
leave  the  glass.  The  best  qualities,  however,  will  be  less 
liable. 

BLACK  VARNISH — Is  readily  prepared  by  adding  a  small 
quantity  of  lampblack  to  gold-size  and  mixing  intimately. 
Dr.  Carpenter  recommends  this  as  a  good  finishing  varnish, 
drying  quickly  and  being  free  from  that  brittleness  which 
renders  some  of  the  others  almost  worthless ;  but  it  should 
not  be  used  in  the  first  process  when  mounting  objects  in 
fluid. 

Amongst  these  different  cements  and  varnishes  I  worked 
a  long  time  without  coming  to  any  decision  as  to  their 
comparative  qualities,  though  making  innumerable  experi- 
ments. The  harder  kinds  were  continually  cracking,  and 
the  softer  possessed  but  little  adhesive  power.  To  find 
hardness  and  adhesiveness  united  was  my  object,  and  the 
following  possesses  these  qualities  in  a  great  degree : — 

India-rubber    ^  drachm. 

Asphaltum  4  oz. 

Mineral  naphtha 10    „ 

Dissolve  the  india-rubber  in  the  naphtha,  then  add  the 
asphaltum — if  necessary,  heat  must  be  employed. 

Some  scientific  friends  have  complained  that  they  have 
been  unable  to  dissolve  either  the  india-rubber  or  the 
asphaltum  in  mineral  naphtha.  The  frequency  with  which 
I  have  seen  this  solution  thoroughly  accomplished  convinces 


OF   MICROSCOPIC   OBJECTS.  49 

me  that  one  of  these  things  has  occurred — either  the  india- 
rubber  or  the  asphaltum  has  not  been  pure,  or  the  naphtha 
has  been  wood  instead  of  mineral.  In  the  early  photo- 
graphic days  every  artist  made  a  form  of  this  varnish  to 
use  with  glass  positives,  and  I  never  heard  a  complaint  of 
difficulty. 

This  is  often  used  by  photographers  as  a  bla,ck  varnish 
for  glass,  and  never  cracks,  whilst  it  is  very  adhesive.  Dr. 
Carpenter,  however,  states  that  his  experience  has  not  been 
favourable  to  it ;  but  I  have  used  it  in  great  quantities  and 
have  never  found  it  to  leave  the  glass  in  a  single  instance 
when  used  in  the  above  proportions.  The  objections  to  it 
are,  however,  I  think  easily  explained,  when  it  is  known 
that  there  are  many  kinds  of  pitch,  &c.,  from  coal,  sold  by 
the  name  of  asphaltnm,  some  of  which  are  worthless  in 
making  a  microscopic  cement.  When  used  for  this  purpose, 
the  asphaltum  must  be  genuine  and  of  the  best  quality 
that  can  be  bought.  The  above  mixture  serves  a  double 
purpose — to  unite  the  cell  to  the  slide,  and  also  as  a  "finish- 
ing "  varnish.  But  it  is  perhaps  more  convenient  to  have 
two  bottles  of  this  cement,  one  of  which  is  thicker  than 
common  varnish,  to  use  for  uniting  the  cell,  &c. ;  the  other 
liquid  enough  to  flow  readily,  which  may  be  employed  as  a 
surface  varnish  in  finishing  the  slides. 

The  brushes  or  camel-hair  pencils  should  always  be 
cleaned  after  use ;  but  with  the  asphalt  varnish  above 
mentioned  it  is  sufficient  to  wipe  off  as  carefully  as  possible 
the  superfluous  quantity  which  adheres  to  the  pencil,  as. 
when  again  used,  the  varnish  will  readily  soften  it ;  but,  of 
course,  it  will  be  necessary  to  keep  separate  brushes  for 
certain  purposes. 

Here  it  may  be  observed  that  every  object  should  be 
labelled  with  name  and  any  other  descriptive  item  as  soon 
as  mounted.  There  are  many  little  differences  in  the 
methods  of  doing  this.  Some  write  with  a  diamond  upon 
the  slide  itself;  but  this  has  the  disadvantage  of  being  not 
so  easily  seen.  For  this  reason  a  small  piece  of  paper  is 

£ 


50  PKEPARATION    AND    MOUNTING 

usually  affixed  to  one  end  of  the  slide,  on  which  is  written 
what  is  required.  These  labels  may  be  bought  of  different 
colours  and  designs;  but  the  most  simple  are  quite  as  good, 
and  very  readily  procured.  Take  a  sheet  of  thin  writing 
paper  and  brush  over  one  side  a  strong  solution,  of  gum, 
with  the  addition  of  a  few  drops  of  glycerine,  or  grains  of 
moist  sugar,  as  above  recommended ;  allow  this  to  dry,  and 
then  with  a  common  gun-punch  stamp  out  the  circles, 
which  may  be  affixed  to  the  slides  by  simply  damping  the 
gummed  surface,  taking  care  to  write  the  required  name, 
&c.,  upon  it  before  damping  it,  or  else  allowing  it  to  become 
perfectly  dry  first. 

There  is  one  difficulty  which  a  beginner  often  experiences 
in  sorting  and  mounting  certain  ^specimens  under  the  micro- 
scope, viz.,  the  inversion  of  the  objects ;  and  it  is  often 
stated  to  be  almost  impossible  to  work  without  an  erector. 
But  this  difficulty  soon  vanishes,  the  young  student  becoming 
used  to  working  what  at  first  seems  in  contradiction  to  his 
eight. 

Let  it  be  understood,  that  in  giving  the  description  of 
those  articles  which  are  usually  esteemed  necessary  in  the 
various  parts  of  microscopic  manipulation,  I  do  not  mean  to 
say  that  without  many  of  these  no  work  of  any  value  can 
be  done.  There  are,  as  all  will  allow,  certain  forms  of 
apparatus  which  aid  the  operator  considerably;  but  the 
cost  may  be  too  great  for  him.  A  little  thought,  however, 
will  frequently  overcome  this  difficulty,  by  enabling  him  to 
make,  or  get  made,  for  himself,  at  a  comparatively  light 
expense,  something  which  will  accomplish  all  he  desires. 
As  an  example  of  this,  a  friend  of  mine  made  what  he  terms 
his  "  universal  stand,"  to  carry  various  condensers,  &c.  &c., 
in  the  following  way : — Take  a  steel  or  brass  wire,  three- 
sixteenths  or  one-quarter  inch  thick  and  six  or  eight  inches 
long;  "tap"  into  a  solid,  or  make  rough  and  fasten  with 
melted  lead  into  a  hollow,  ball.  (The  foot  of  a  cabinet 
or  work-box  answers  the  purpose  very  well.)  In  the  centre 
of  a  round  piece  of  tough  board,  three  inches  in  diameter, 


OF   MICROSCOPIC   OBJECTS.  51 

make  a  hemispherical  cavity  to  fit  half  of  the  ball,  and  bore 
a  hole  through  from  the  middle  of  this  cavity,  to  allow  the 
wire  to  pass.  Take  another  piece  of  board,  about  four  inches 
in  diameter,  either  round  or  square,  and  one  and  a  half  or 
two  inches  thick,  make  a  similar  cavity  in  its  centre  to 
receive  the  other  half  of  the  ball,  but  only  so  deep  as  to 
allow  the  ball  to  fit  tightly  when  the  two  pieces  of  board 
are  screwed  together,  which  last  operation  must  be  done  with 
three  or  four  screws.  L^t  the  hole  for  the  wire  in  the  upper 
part  be  made  conical  (base  upwards),  and  so  large  as  only 
to  prevent  the  ball  from  escaping  from  its  socket,  in  order 
that  the  shaft  may  move  about  as  freely  as  possible.  Turn 
a  cavity,  or  make  holes,  in  the  bottom  of  the  under  piece, 
and  fill  with  lead  to  give  weight  and  steadiness.  This, 
painted  green  bronze  and  varnished,  looks  neat ;  and  by 
having  pieces  of  gutta-percha  tubing  to  fit  the  shaft,  a  great 
variety  of  apparatus  may  be  attached  to  it. 

Mr.  Loy  employs  the  following  arrangement  for  dissecting 
insects  or  picking  out  Foraminifera,  &c. :  he  fits  an  upright 
brass  rod  into  a  heavy  leaden  foot,  this  rod  carries  a  hori- 
zontal arm  bearing  at  its  end  a  ring  for  holding  a  watch- 
maker's eye-glass;  in  focussing  it  to  his  work,  he  presses 
the  eye-glass  down  with  his  head,  the  weight  of  the  leaden 
foot  keeping  it  in  its  place,  and  allowing  it  to  follow  his 
every  movement. 

Again,  a  "condenser"  is  often  required  for  the  illumina- 
tion of  opaque  objects.  My  ingenious  friend  uses  an 
"  engraver's  bottle "  (price  6d.),  fills  it  with  water,  and 
suspends  it  betwixt  the  light  and  the  object.  Where  the 
light  is  very  yellow,  he  tints  the  water  with  indigo,  and  so 
removes  the  objectionable  colour. 

I  merely  mention  these  as  examples  of  what  may  be 
done  by  a  little  thoughtful  contrivance,  and  to  remove  the 
idea  that  nothing  is  of  much  value  save  that  which  is  the 
work  of  professional  workmen,  and  consequently  expensive. 


52  PREPARATION    AND   MOUNTING 


CHAPTER     III. 

TO   PREPARE   AND   MOUNT   OBJECTS    "DRY." 

THE  terra  "dry"  ia  used  when  the  object  to  be  mounted  is 
not  immersed  in  any  liquid  or  medium,  but  preserved  in  its 
natural  state,  unless  it  requires  cleaning  and  drying. 

I  have  before  stated  that  thorough  cleanliness  is  necessary 
in  the  mounting  of  all  microscopic  objects.  I  may  here  add 
that  almost  every  kind  of  substance  used  by  the  microscopist 
suffers  from  careless  handling.  Many  leaves  with  fine  hairs 
are  robbed  of  half  their  beauty,  or  the  hairs,  perhaps,  forced 
into  totally  different  shapes  and  groups;  many  insects  lose 
their  scales,  which  constitute  their  chief  value  to  the  micro- 
scopist ;  even  glass  itself  distinctly  shows  the  marks  of  the 
fingers  if  left  uncleaned.  Every  object  must  also  be 
thoroughly  dry,  otherwise  dampness  will  arise  and  become 
condensed  in  small  drops  upon  the  inner  surface  of  the  thin 
glass  cover.  This  defect  is  frequently  met  with  in  slides 
which  have  been  mounted  quickly ;  the  objects  not  being 
thoroughly  dry  when  enclosed  in  the  cell.  Many  cheap 
slides  are  thus  rendered  worthless.  Even  with  every  care 
it  is  not  possible  to  get  rid  of  this  annoyance  occasionally. 
A  good  plan  is  to  fix  the  covers  on  to  the  cells  temporarily 
by  dropping  on  two  sides  of  them  a  composition  of  equal 
parts  of  wax  and  resin :  this  allows  of  the  easy  removal  of 
the  cover  at  any  time,  while  the  object  thoroughly  dries 
and  is  protected  from  dust  and  damage. 

For  the  purpose  of  mounting  opaque  objects  "  dry " 
discs  were  at  one  time  very  commonly  used.  These  are 
circular  pieces  of  cork,  leather,  or  other  soft  substance,  from, 
one-quarter  to  half  an  inch  in  diameter,  blackened  with  varnish 


OF   MICROSCOPIC   OBJECTS.  53 

or  covered  with  black  paper,  on  which  the  object  is  fixed  by 
gum  or  some  other  adhesive  substance.  They  are  usually 
pierced  longitudinally  by  a  strong  pin,  which  serves  for  the 
forceps  to  lay  hold  of  when  being  placed  under  the  micro- 
scope for  examination.  Sometimes  objects  are  affixed  to 
both  sides  of  the  disc,  which  is  readily  turned  when  under 
the  ohject-glass.  The  advantage  of  this  method  of  mount^ 
ing  is  the  ease  with  which  the  disc  may  be  moved,  and  so 
present  every  part  of  the  object  to  the  eye,  save  that  by 
which  it  is  fastened  to  the  disc.  On  this  account  it  is  often 
used  when  some  particular  subject  is  undergoing  investiga- 
tion, as  a  number  of  specimens  may  be  placed  upon  the 
discs  with  very  little  labour,  displaying  all  their  parts.  But 
where  exposure  to  the  atmosphere  or  small  particles  of  dust 
will  injure  an  object,  no  advantage  which  discs  may  possess 
should  be  considered,  and  an  ordinary  covered  cell  should 
be  employed.  Small  pill-boxes  have  been  used,  to  the  bot- 
tom of  which  a  piece  of  cork  has  been  glued  to  afford  a 
ground  for  the  pin  or  other  mode  of  attachment;  but  thia 
is  liable  to  some  of  the  same  faults  as  the  disc,  and  it  would 
be  unwise  to  use  these  for  permanent  objects. 

Messrs.  Smith  and  Beck  have  lately  invented,  and  are 
now  making  a  beautiful  small  apparatus,  by  means  of 
which  the  disc  supporting  the  object  can  be  worked  with 
little  or  no  trouble  into  any  position  that  may  prove  most 
convenient,  whilst  a  perforated  cylinder  serves  for  the  recep- 
tion of  the  discs  when  out  of  use,  and  fits  into  a  case  to 
protect  them  from  dust.  A  pair  of  forceps  is  made  for  the 
express  purpose  of  removing  them  from  the  case  and  placing 
them  in  the  holder. 

All  dry  objects,  however,  which  are  to  be  preserved  should 
be  mounted  on  glass  slides  in  one  of  the  cells  (described  in 
Chapter  II.)  best  suited  to  them.  "Where  the  object  is  to  be 
free  from  pressure,  care  must  be  taken  that  the  cell  is  deep 
enough  to  ensure  this.  When  the  depth  required  is  but 
small,  it  is  often  sufficient  to  omit  the  card,  leather,  or 
other  circles,  and  with  the  "  turntable  "  before  described  by 


54  PREPARATION   AND   MOUNTING 

means  of  a  thick  varnish  and  camel-hair  pencil,  to  form  a 
ring  of  the  desired  depth ;  but  should  the  varnish  not  be  of 
sufficient  substance  to  give  such  "  walls  "  at  onr.e,  the  first 
application  may  be  allowed  to  dry,  and  a  second  made  upon 
it.  A  number  of  these  may  be  prepared  at  the  same  time, 
and  laid  by  for  use.  When  liquids  are  used  (see  Chapter  V.), 
Dr.  Carpenter  recommends  gold-size  as  a  good  varnish 
for  the  purpose,  and  this  may  be  used  in  dry  mountings 
also.  I  have  used  the  asphaltutu  and  india-rubber  (men- 
tioned in  Chapter  II.),  and  found  it  to  be  everything  I  could 
wish.  The  cells,  however,  must  be  thoroughly  dry,  and  when 
they  will  bear  the  heat  they  should  be  baked  for  an  hour  at 
least  in  a  tolerably  cool  oven,  by  which  treatment  the  latter 
becomes  an  excellent  medium.  All  dry  objects  which  will 
not  bear  pressure  must  be  firmly  fastened  to  the  slide, 
otherwise  the  necessary  movements  often  injure  them, 
by  destroying  the  fine  hairs,  &c.  For  this  purpose  thin 
varnishes  are  often  used,  and  will  serve  well  enough  for 
large  objects,  but  many  smaller  ones  are  lost  by  adopting 
this  plan,  as  for  a  time,  which  may  be  deemed  long  enough 
to  harden  the  varnish,  they  exhibit  no  defect,  but  in  a  while 
a  "wall"  of  the  plastic  gum  gathers  around  them,  which 
refracts  the  light,  and  thus  leads  the  student  to  false 
conclusions.  In  all  finer  work,  where  it  is  necessary  to 
use  any  method  of  fixing  them  to  the  slide,  a  solution  of 
common  gum,  with  the  addition  of  a  few  drops  of  glycerine 
(Chapter  II.),  will  be  found  to  serve  the  purpose  perfectly. 
It  must,  however,  be  carefully  filtered  through  blotting- 
paper,  otherwise  the  minute  particles  in  the  solution  interfere 
with  the  object,  giving  the  slide  a  dusty  appearance  when 
under  the  microscope. 

When  mounting  an  object  in  any  of  these  cells,  the  glass 
must  be  thoroughly  cleaned,  which  may  be  done  with  a 
cambric  handkerchief,  after  the  washing  mentioned  in  Chap- 
ter II.  If  the  object  be  large,  the  point  of  a  fine  camel-hair 
pencil  should  be  dipped  into  the  gum  solution,  and  a  minute 
quantity  of  the  liquid  deposited  in  the  cell  where  the  object 


OF   MICROSCOPIC   OBJECTS.  55 

is  to  be  placed,  but  not  to  cover  a  greater  surface  than  the 
object  will  totally  hide  from  sight.  This  drop  of  gum  must 
be  allowed  to  dry,  which  will  take  a  few  minutes.  Breathe 
then  upon  it  two  or  three  times,  holding  the  slide  not  far 
from  the  mouth,  which  will  render  the  surface  adhesive. 
Then  draw  a  camel-hair  pencil  through  the  lips,  so  as  to 
moisten  it  slightly  (when  anything  small  will  adhere  to 
it  quite  firmly  enough),  touch  the  object  and  place  it 
upon  the  gum  in  the  desired  position.  This  must  be  done 
immediately  to  ensure  perfect  stability,  otherwise  the  gum 
will  become  at  least  partially  dry  and  only  retain  the  object 
imperfectly. 

When,  however,  the  objects  are  so  minute  that  it  would 
be  impossible  to  deposit  atoms  of  gum  small  enough  for 
each  one  to  cover,  a  different  method  of  proceeding  must  be 
adopted.  In  this  case  a  small  portion  of  the  same  gum 
solution  should  be  placed  upon  the  slide,  and  by  means  of 
any  small  instrument — a  long  needle  will  serve  the  purpose 
very  well — spread  over  the  surface  which  will  be  required. 
The  quantity  thus  extended  will  be  very  small,  but  by 
breathing  upon  it  may  be  prevented  drying  whilst  being 
dispersed.  This,  like  the  forementioned,  should  be  then 
allowed  to  dry ;  and  whilst  the  objects  are  being  placed  on 
the  prepared  surface,  breathing  upon  it  as  before  will  restore 
the  power  of  adherence.  A  small  patch  of  gold-size — or 
gum  dammar  solution  which  has  been  allowed  to  become 
"tackey" — is  very  useful  in  many  cases. 

When  gum  or  other  liquid  cement  has  been  used  to  fix 
the  objects  to  the  glass,  the  thin  covers  must  not  be  applied 
until  the  slide  has  been  thoroughly  dried,  and  all  fear  of 
dampness  arising  from  the  use  of  the  solution  done  away 
•with.  Warmth  may  be  safely  applied  for  the  purpose,  as 
objects  fastened  by  this  method  are  seldom,  if  ever  found  to 
be  loosened  by  it.  As  objects  are  met  with  of  every  thick- 
ness, the  cells  will  be  required  of  different  depths.  There 
is  no  difficulty  in  accommodating  ourselves  in  this — the 
deeper  cells  may  be  readily  cut  out  of  thick  leather,  card,  or 


56  PREPARATION   AND   MOUNTING 

other  substance  preferred  (as  mentioned  in  Chapter  II.). 
Cardboard  is  easily  procured  of  almost  any  thickness ;  but 
sometimes  it  is  convenient  to  find  a  thinner  substance  even 
than  this.  When  thin  glass  is  laid  upon  a  drop  of  any 
liquid  upon  a  slide,  every  one  must  have  observed  how 
readily  the  liquid  spreads  betwixt  the  two :  jnst  so  when 
any  thin  varnish  is  used  to  surround  an  object  of  little  sub- 
stance, excessive  care  is  needed  lest  the  varnish  should 
extend  betwixt  the  cover  and  slide,  and  so  render  it  worth- 
less. The  slightest  wall,  however,  prevents  this  from  taking 
place,  so  that  a  ring  of  common  paper  may  be  used,  and 
serve  a  double  purpose  where  the  objects  require  no  deeper 
cell  than  this  forms. 

Many  objects,  however,  are  of  such  tenuity — as  the  leaves 
of  many  naosse?,  some  of  the  Diatomaceae,  scales  of  insects, 
&c. — that  no  cell  is  requisite  excepting  that  which  is  neces- 
sarily formed  by  the  medium  used  to  attach  the  thin  glass 
cover  to  the  slide ;  and  where  the  slide  is  covered  by  the 
ornamental  papers  mentioned  in  Chapter  II.,  and  pressure 
does  not  injure  the  object,  even  this  is  omitted,  the  thin 
glass  being  kept  in  position  by  the  cover ;  but  slides  mounted 
in  this  manner  are  frequently  injured  by  dampness,  which 
soon  condenses  upon  the  inner  surfaces  and  interferes  both 
with  the  object  and  the  clearness  of  its  appearance. 

The  thin  glass,  then,  is  to  be  united  to  the  slide,  so  as  to 
form  a  perfect  protection  from  dust,  dampness,  or  other 
injurious  matter,  and  yet  allow  a  thoroughly  distinct  view 
of  the  object.  This  is  to  be  done  by  applying  to  the  glass 
slide  round  the  object  some  adhesive  substance,  and  with  the 
forceps  placing  the  thin  glass  cover  (quite  dry  and  clean) 
upon  it.  A  gentle  pressure  round  the  edge  will  then 
ensure  a  perfect  adhesion,  and  with  ordinary  care  there  will 
be  little  or  no  danger  of  breakage.  For  this  purpose  gold- 
size  is  frequently  used.  The  asphalt  and  india-rubber 
varnish  also  will  be  found  both  durable  and  serviceable. 
Whatever  cement  may  be  used,  it  is  well  to  allow  it  to 
become  in  some  measure  fixed  and  dried ;  but  where  no 


OF   MICROSCOPIC    OBJECTS.  57 

cell  or  wall  is  upon  the  slide,  this  is  quite  necessary, 
otherwise  the  varnish  will  be  most  certain  to  extend,  as 
before  mentioned,  and  ruin  the  object.  It  may  be  stated 
here  that  gold-size  differs  greatly  in  its  drying  powers, 
according  to  its  age,  mode  of  preparation,  &c.  (Chapter  V.) : 
here  gum  dammar  solution  laid  on  in  a  very  thin  coating 
will  be  found  most  useful,  as  it  dries  so  rapidly  that  it  cannot 
run  in  unless  laid  on  with  an  unsparing  hand. 

Should  any  object  be  enclosed  which  requires  to  be  kept 
flat  during  the  drying  of  the  cement,  it  will  be  necessary  to 
use  some  of  the  contrivances  mentioned  iu  Chapter  II. 

When  the  slide  is  thus  far  advanced,  there  remains  the 
finishing  only.  Should  the  student",  however,  have  no 
time  to  complete  his  work  at  once,  he  may  safely  leave  it  at 
this  stage  until  he  have  a  number  of  slides  which  he  may 
finish  at  the  same  time.  There  are  different  methods  of 
doing  this,  some  of  which  may  be  here  described. 

If  ornamental  papers  are  preferred,  a  small  circle  must 
be  cut  out  from  the  centre  a  little  less  than  the  thin  glass 
which  covers  the  object.  Another  piece  of  coloured  paper 
is  made  of  the  same  size,  and  a  similar  circle  taken  from  its 
centre  also,  or  both  may  be  cut  at  the  same  time.  The 
slide  is  then  covered  round  the  edges  with  paper  of  any 
plain  colour,  so  that  it  may  extend  about  one-eighth  of  an 
inch  over  the  glass  on  every  side.  The  ornamental  paper 
is  then  pasted  on  the  "  object "  surface  of  the  glass,  so  that 
the  circle  shows  the  object  as  nearly  in  the  centre  as  possible, 
and  covers  the  edges  of  the  thin  glass.  The  other  coloured 
paper  is  then  affixed  underneath  with  the  circle  coinciding 
with  that  above.  And  here  I  may  observe,  that  when  this 
method  is  used  there  is  no  necessity  for  the  edges  of  the 
slide  to  be  ground,  as  all  danger  of  scratching,  &c.,  is 
obviated  by  the  paper  cover. 

Many  now  use  paper  covers,  about  one  and  a  half  inch 
long,  on  the  upper  side  of  the  slide  only,  with  the  centre 
cut  out  as  before,  with  no  other  purpose  than  that  of 
hiding  the  edge  of  the  thin  glass  where  it  is  united  to  the  slide. 


58  PREPARATION   AND   MOUNTING 

The  method  of  finishing,  however,  which  is  mostly  used 
at  the  present  time,  is  to  lay  a  coating  of  varnish  upon  the 
edge  of  the  thin  glass,  and  extend  it  some  little  way  on  the 
slide.  When  a  black  circle  is  required,  nothing  serves  the 
purpose  better  than  the  gold-size  and  lampblack,  or  the 
asphalt  and  india-rubber  varnish,  neither  of  which  is  liable 
to  chip;  but  when  used  for  this,  the  latter  should  be  rather 
thinner,  as  before  advised.  Some  of  these  varnishes  are 
preferred  of  different  colours,  which  may  be  made  by  using 
the  different  kinds  of  selling-wax,  as  described  in  Chapter  II.; 
but  they  are  always  liable  to  the  defects  there  mentioned. 
This  circle  cannot  be  made  in  any  other  way  than  by  one  of 
those  contrivances  called  turntables.  A  very  little  practice 
will  enable  the  young  student  to  place  his  slide  so  that  the 
circle  may  be  uniform  with  the  edge  of  the  thin  glass. 

The  slide  is  now  complete,  except  the  addition  of  the 
name  and  any  other  particulars  which  may  be  desirable. 
For  this  purpose  one  of  the  methods  described  in  Chapter  II, 
must  be  employed. 

Amongst  the  various  classes  of  microscopic  objects  now 
receiving  general  attention,  the  Diatomaceae  may  be  placed 
in  a  prominent  position.  They  afford  endless  opportunities 
of  research,  and  some  very  elaborate  works  have  already 
been  issued  concerning  them.  Professor  Smith's  may  be 
mentioned  as  one  containing,  perhaps,  the  best  illustrations. 
The  young  student  may  wish  to  know  what  a  diatom  is. 
The  "  Micrographic  Dictionary "  gives  the  following  defi- 
nition : — "  A  family  of  confervoid  Algae,  of  very  peculiar 
character,  consisting  of  microscopic  brittle  organisms." 
They  are  now  looked  upon  by  almost  all  of  our  scientific 
men  as  belonging  to  the  vegetable  kingdom,  though  some 
few  still  assign  them  to  the  animal.  They  are  almost 
invariably  so  exceedingly  small,  that  the  unaided  eye  can 
perceive  nothing  on  a  prepared  slide  of  these  organisms  but 
minute  dust.  Each  separate  portion,  which  is  usually  seen 
when  mounted,  is  termed  a  "  frustule,"  or  "  te,-tnle :"  this 
consists  of  two  similar  parts,  composed  of  silica,  between  and 


OF   MICROSCOPIC   OBJECTS.  59 

sometimes  around  which,  is  a  mass  of  viscid  matter  called 
the  "  endochrome."  They  are  found  in  almost  every  descrip- 
tion of  water,  according  to  the  variety :  some  prefer  sea- 
water,  others  fresh,  and  many  are  seen  nowhere  but  in  that 
which  is  a  mixtiire  of  both,  as  the  mouths  of  rivers,  &c. 
Ditches,  ponds,  cisterns,  and  indeed  almost  every  reservoir, 
yield  abundance  of  these  forms.  They  are  not,  however, 
confined  to  "present"  life;  but,  owing  to  the  almost  in- 
destructible nature  of  their  siliceous  covering,  they  are 
found  in  a  fossil  state  in  certain  earths  in  great  abundance, 
and  are  often  termed  "  fossil  Infusoria."  Upon  these  frus- 
tules  are  generally  to  be  seen  lines,  or  markings,  of 
different  degrees  of  minuteness,  the  delicacy  of  which  often 
serves  the  purpose  of  testing  the  defining  power  of  object-; 
glasses.  Some  of  the  frustules  are  triangular,  others  circular, 
and,  indeed,  of  almost  every  conceivable  shape,  many  of 
them  presenting  us  with  exquisitely  beautiful  designs. 

The  markings,  however,  are  seldom  seen  well,  if  at  all, 
until  the  frustules  are  properly  prepared,  the  different 
methods  of  accomplishing  which  will  be  given  a  little 
further  on. 

The  collection  of  fresh,  diatoms  is  so  closely  connected 
with  their  preservation,  that  a  few  notes  may  be  given  upon 
it  before  we  pass  on.  For  this  purpose  a  number  of  small 
bottles  must  be  provided,  which  may  be  placed  in  a  tin  box, 
with  a  separate  compartment  for  each,  so  that  all  chance  of 
breakage  may  be  done  away  with.  The  diatoms  are  generally 
of  a  light  brown  colour;  and  where  they  are  observed  in  the 
water,  the  bottle  may  be  so  placed,  with  the  mouth  closed 
by  the  finger,  that  when  the  finger  is  withdrawn  the  water 
will  rush  in,  carrying  the  diatoms  also.  If  they  are  seen 
upon  plants,  stones,  or  any  other  substance,  they  may 
generally  be  detached  and  placed  in  the  bottle.  When 
there  is  a  green  covering  upon  the  surface  of  the  water,  a 
great  quantity  of  diatoms  is  usually  found  amongst  it;  as 
also  upon  the  surface  of  the  mud  in  those  ponds  where  they 
abound.  In  these  cases,  a  broad  flat  spoon  will  be  found 


60  PREPARATION   AND    MOUNTING 

very  useful,  and  one  is  now  made  with  a  covering  upon  the 
broader  portion  of  it  to  protect  the  enclosed  matter  from 
being  so  readily  carried  off  whilst  bringing  it  to  the  surface 
again.  Where  there  is  any  depth  of  water,  and  the  spoon 
•will  not  reach  the  surface  of  the  mud,  the  bottle  must  be 
united  to  a  long  rod,  and  being  then  carried  through  the 
upper  portion  with  the  mouth  downwards,  no  water  will  be 
received  into  it ;  but  on  reaching  the  spot  required,  the 
bottle-mouth  may  be  turned  up,  and  thus  become  tilled  with 
what  is  nearest. 

From  the  stomachs  of  common  fish — as  the  cod,  sole,  had- 
dock, &c. — many  specimens  of  Diatomaceae  may  be  obtained, 
but  especially  from  the  crab,  oyster,  mussel,  and  other  shell- 
fish. Professor  Smith  states  that  from  these  curious  recep- 
tacles he  has  taken  some  with  which  he  has  not  elsewhere 
met.  To  remove  them  from  any  of  the  small  shell-fish,  it  is 
necessary  to  take  the  fish  or  stomach  from  the  shell,  and 
immerse  it  in  strong  hot  acid  (nitric  is  the  best)  until  the 
animal  matter  is  dissolved,  when  the  residue  must  be 
washed  and  treated  as  the  ordinary  Diatomaceas  hereinafter 
described. 

Many  diatoms  are  seen  best  when  mounted  in  a  dry 
state,  the  minute  markings  becoming  much  more  indistinct 
if  immersed  in  liquid  or  balsam ;  and  for  this  reason  those 
which  are  used  as  test  objects  are  usually  mounted  dry. 
Many  kinds  are  also  now  prepared  in  this  way  as  opaque 
objects,  to  be  examined  with  the  lieberkuhn,  and  are  ex- 
quisitely beautiful.  Others,  however,  are  almost  invariably 
mounted  in  balsam ;  but  as  these  will  be  again  referred  to 
in  Chapter  IV.,  and  require  the  same  treatment  to  fit  them 
for  the  slide,  it  will  not  be  out  of  place  to  describe  the 
cleaning  and  preparation  of  them  here.  As  before  stated, 
there  is  much  matter  surrounding  them  which  must  be 
got  rid  of  before  the  siliceous  covering  can  be  shown 
perfectly.  As,  however,  vre  may  first  wish  to  become 
acquainted  in  some  degree  with  what  we  have  to  do,  it  is 
well  to  take  a  small  piece  of  talc,  and  place  a  few  of  the 


OF   MICROSCOPIC   OBJECTS.  61 

diatoms  upon  it.  This  may  be  held  over  the  flame  of  the 
spirit-lamp  until  all  the  surrounding  matter  is  burnt  away, 
and  a  tolerable  idea  may  thus  be  obtained  as  to  the  quality 
of  our  treasure. 

In  some  cases  it  is  well  to  use  this  burning  operation 
alone  in  mounting  specimens  of  diatoms,  when  they  may  be 
placed  in  their  natural  state  upon  thin  glass,  burnt  for 
awhile  upon  the  platinum  plate,  hereinafter  described,  and 
mounted  dry  or  in  balsam. 

In  the  preparation  and  cleaning  of  Diatomaceae,  there  is 
little  satisfaction  unless  these  operations  have  been  success- 
fully performed,  as  a  very  small  portion  of  foreign  matter 
seriously  interferes  with  the  object.  The  mode  of  preparing 
them  varies  even  amongst  the  most  experienced.  It  will  be 
found,  therefore,  most  satisfactory  to  examine  the  principal 
of  these  separately,  although  it  may  be  at  the  risk  of  some 
little  repetition. 

The  method  which  is  most  frequently  employed  is  the 
following : — Place  the  gathering  containing  the  Diato- 
maceaB  in  a  small  glass  or  porcelain  vessel,  add  strong 
nitric  acid,  and,  by  the  aid  of  a  Bunsen's  burner  or  spirit- 
lamp,  boil  for  some  minutes.  From  time  to  time  a  drop  of 
the  mixture  may  be  put  upon  a  slide,  and  examined  under 
the  microscope  to  see  if  all  foreign  matter  be  got  rid  of. 
When  the  valves  are  clean,  the  vessel  containing  them  must 
be  filled  with  water,  and  the  whole  lefb  for  an  hour  or  two, 
so  that  all  the  diatoms  may  settle  perfectly.  The  liquid 
must  then  be  poured  off  carefully,  or  drained  away  by  the 
aid  of  a  syphon,  so  that  none  of  the  diatoms  are  removed 
with  it.  Indeed,  it  is  well  to  examine  the  liquid  drained  off 
each  time  with  the  microscope,  as  the  finer  forms  are 
frequently  lost  in  the  washings.  The  vesselmust  then  be 
refilled  with  pure  water,  allowed  to  settle,  and  drained  as 
before.  This  washing  must  be  repeated  until  a  drop  being 
placed  upon  a  slide  and  evaporated  leaves  no  crystals. 
When  it  is  desirable  to  preserve  the  diatoms  in  this  state 
before  mounting  (which  process  will  be  described  in  another 


62  PREPARATION   AND   MOUNTING 

place),  they  may  be  placed  in  a  small  phial  with  a  little 
distilled  water. 

There  are  many  cases  in  which  the  above  method  will  not 
effect  a  perfect  cleansing,  as  certain  substances  with  which 
diatoms  are  frequently  mixed  are  not  soluble  in  nitric  acid. 
For  this  reason  the  following  method  is  resorted  to : — Take 
a  quantity  of  the  matter  containing  the  Diatomacese  and 
wash  first  with  pure  water,  to  get  rid  of  all  the  impurities 
possible.  Allow  this  to  settle  perfectly  and  decant  the 
water.  Add  hydrochloric  acid  gradually,  and  when  all 
effervescence  has  subsided,  boil  for  some  minutes  by  aid  of 
the  lamp.  When  cool  and  the  particles  have  subsided, 
decant  the  hydrochloric  and  add  nitric  acid.  The  boiling 
must  then  be  repeated  until  a  drop  of  the  liquid  when 
placed  under  the  microscope  shows  the  valves  or  "  frustules  " 
clean.  After  allowing  the  diatoms  to  settle,  the  acid  must 
be  decanted,  and  pure  water  substituted.  The  washing 
must  be  repeated  as  in  the  former  process  until  all  the 
remains  of  crystals  or  acid  are  removed,  when  the  specimens 
may  be  preserved  in  small  phials. 

Such  are  the  usual  modes  of  treating  the  Diatomaceae, 
but  there  are  certain  cases  in  which  particular  methods  are 
required  to  give  anything  like  perfect  results.  Persons  of 
great  experience  combine  a  variety  of  treatments,  and  thus 
obtain  better  and  more  uniform  specimens.  Perhaps  it  will 
be  advantageous  to  give  the  young  student  the  process 
adopted  by  one  of  the  most  successful  preparers  of  these 
objects ;  but  I  will  first  state  the  different  methods  of 
mounting  the  cleaned  diatoms  dry :  how  to  employ  Canada 
balsam  and  fluid  in  their  preservation  will  be  elsewhere 
described. 

It  was  before  stated  that  diatoms  when  cleansed  might 
be  preserved  in  small  phials  of  distilled  water.  When  re- 
quired for  mounting,  shake  the  phial,  and  with  a  thin  glass 
tube  or  rod  take  up  a  drop  of  the  fluid  and  spread  it  upon 
the  surface  of  the  slide  in  the  desired  position.  This  must 
then  be  allowed  to  dry  gradually,  or  by  the  aid  of  the  lamp 


OF   MICROSCOPIC   OBJECTS.  63 

if  necessary,  without  being  shaken  or  interfered  with,  other- 
wise uniformity  of  dispersion  will  be  prevented.  When 
thoroughly  dry,  a  thin  ring  of  one  of  the  adhesive  varnishes 
— gold-tdze  will  be  found  as  good  as  any — may  be  drawn 
round  the  diatoms,  and  allowed  to  dry  in  a  slight  degree. 
The  slide  and  thin  glass  cover  should  then  be  warmed  and 
the  latter  gently  pressed  upon  the  ring  of  varnish  until  the 
adhesion  all  round  is  complete. 

As  some  of  the  diatoms  require  object-glasses  of  extremely 
high  power,  and  consequently  short  focus,  to  show  them, 
they  must  be  as  close  to  the  outer  surface  of  the  cover  as 
possible.  For  this  reason  they  are  sometimes  placed  upon 
the  under  side  of  the  thin  glass,  as  follows.  Clean  the 
surfaces  of  the  slide  and  cover,  and  with  the  rod  or  pipe 
place  the  liquid  containing  the  diatoms  upon  the  thin  glass, 
and  dry  as  before.  Trace  the  ring  to  receive  the  cover  upon 
the  slide,  and  when  almost  dry,  warm  both  and  proceed  as 
above.  Whichever  of  these  methods  is  employed,  the  outer 
ring  of  coloured  varnish  may  be  applied  as  elsewhere  described 
and  the  slide  finished. 

Diatoms  are  also  sometimes  mounted  betwixt  two  thin 
glasses,  as  described  in  Chapter  II.,  so  that  the  light  by 
which,  they  are  examined  may  receive  as  little  interference  as 
possible,  and  that  an  achromatic  condenser  may  be  brought 
into  focus  under  the  slide. 

Of  the  various  modes  of  cleaning  and  mounting  Diato- 
macea3,  I  believe  that  the  following  may  be  safely  recom- 
mended, as  affording  results  of  the  best  quality.  My  friend, 
Mr.  T.  Gr.  Bylands,  gave  it  to  me  as  that  which  he  prefers, 
and  I  can  safely  say  that  his  numerous  slides  are  at  least 
equal  to  any  I  have  ever  seen.  I  will  give  it  juet  as  I 
received  it  from  him,  though  there  may  be  some  little 
repetition  of  what  has  been  said  elsewhere,  as  he  does  not 
appropriate  any  part  of  it  as  his  own.  He  says  : — In  this 
branch  of  mounting,  general  rules  alone  can  be  laid  down, 
because  the  gatherings  may  contain  iron,  lime,  fine  silt,  or 
vegetable  matter  under  conditions  for  special  treatment,  and 


64  PREPAKATION  AND  MOUNTING 

consequently  the  first  step  should  be  to  experiment  on 
various  kinds. 

In  gathering  diatoms  much  labour  is  saved  by  judgment 
and  care ;  hence  it  is  desirable  to  get  acquainted  with  them 
in  their  growing  condition,  so  that  when  recognised  upon 
the  sand  or  other  spots,  they  may  be  carefully  removed  by 
the  aid  of  the  spoon  or  small  tin  scoop  before  described. 
When  growing  upon  algae  or  other  plants,  the  plants  and 
diatoms  together  may  be  carried  home,  in  which  case  they 
must  be  simply  drained  and  not  washed  or  pressed,  in  order 
that  the  diatoms  be  not  lost.  As  it  is  always  desirable  to 
examine  the  gathering  on  the  ground,  a  "  Gairdner's  hand 
microscope"  with  powers  from  80  to  200  diameters  will  be 
found  very  useful.  The  best  gatherings  are  those  which 
represent  one  species  abundantly.  Those  which  are  mixed 
may  be  rejected,  unless  they  are  seen  to  contain  something 
valuable  or  important,  as  the  object  should  be  not  so  much 
to  supply  microscopical  curiosities  as  to  collect  material  which 
is  available  for  the  study  of  nature. 

The  gathering  when  carried  home  should  always  be  care- 
fully examined  before  anything  is  done  with  it;  not  only  on 
account  of  the  additional  information  thus  acquired,  but 
also  because  it  often  happens  that  a  specimen  should  be 
mounted  in  fluid  (see  Chapter  V.)  in  the  condition  in  which 
it  is  gathered,  as  well  as  cleaned  and  mounted  in  balsam 
(Chapter  IV.)  and  dry. 

Where  the  gathering  is  taken  from  sand,  the  whole  may 
be  shaken  up  in  water  as  a  preliminary  operation,  when 
much  of  the  sand  will  be  separated  by  its  own  weight.  The 
lime  test,  however,  should  be  applied  ;  viz. — a  small  portion 
of  hydrochloric  acid,  and  if  there  be  effervescence,  it  must  be 
dissolved  out  by  this  means.  From  Algae  and  other  weeds 
diatoms  may  be  detached  by  agitating  the  whole  together 
in  a  weak  solution  of  nitrie  acid — about  one  of  pure  acid  to 
twenty  or  thirty  of  water,  as  it  must  be  sufficiently  weak  to 
free  the  diatoms  without  destroying  the  matter  to  which 
they  adhere.  The  diatoms  may  then  be  separated  by 


OF  MICROSCOPIC   OBJECTS.  65 

sifting  through,  coarse  muslin,  which  will  retain  the  Algee, 
&c.  The  process  of  cleaning  will  vary  according  to  circum- 
stances. Some  gatherings  require  to  be  boiled  only  a  few 
minutes  in  nitric  acid;  but  the  more  general  plan,  where 
they  are  mixed  with  organic  or  other  foreign  matter,  is  to 
boil  them  in  pure  sulphuric  acid  until  they  cease  to  grow 
darker  in  colour  (usually  from  a  half  to  one  minute),  aud  then 
to  add,  drop  by  drop  to  avoid  explosions,  a  cold  saturated 
solution  of  chlorate  of  potash  until  the  colour  is  discharged, 
or,  in  case  the  colour  does  not  disappear,  the  quantity  of 
the  solution  used  is  at  least  equal  to  that  of  the  acid. 
This  operation  is  best  performed  in  a  wide-mouthed  ordinary 
beaker  glass,*  a  test-tube  being  too  narrow.  The  mixture 
whilst  boiling  should  be  poured  into  thirty  times  its  bulk  of 
cold  water,  and  the  whole  allowed  to  subside.  The  fluid 
must  then  be  carefully  decanted  and  the  vessel  re-supplied 
once  or  twice  with  pure  water,  so  as  to  get  rid  of  all  the 
acid.  The  gathering  may  then  be  transferred  to  a  small 
boiling-glass  or  test-tube,  and — the  water  being  carefully 
decanted — boiled  in  the  smallest  available  quantity  of 
nitric  acid,  and  washed  as  before.  This  last  process  has 
been  found  necessary  from  the  frequent  appearance  of 
minute  crystals,  which  cannot  otherwise  be  readily  dis- 
posed of  without  the  loss  of  a  considerable  proportion  of 
diatoms. 

I  may  here  mention  that  the  washing-glasses  used  by 
Mr.  Rylands  are  stoppered  conical  bottles  varying  in 
capacity  from  two  ounces  to  one  quart ;  the  conical  form 
being  employed  to  prevent  the  adherence  of  anything  to  the 
side :  they  are  stoppered,  to  render  them  available  in  the 
shaking  process  about  to  be  described. 

The  gathering,  freed  from  acid,  is  now  put  into  two  inches 
depth  of  water,  shaken  vigorously  for  a  minute  or  two,  and 
allowed  to  subside  for  half  an  hour,  after  which  the  turbid 

*  These  glasses  are  round,  about  six  inches  high,  and  usually  contain 
about  eight  ounces.  They  are  rather  wider  at  the  bottom,  tapering 
gradually  to  the  top,  and  may  be  generally  procured  at  the  chemists,  &c. 


66  PREPARATION   AND   MOUNTING 

fluid  must  be  carefully  decanted.  This  operation  must  be 
repeated  until  all  the  matter  is  removed  which  will  not 
settle  in  half  an  hour.  The  fluid  removed  should  be  ex- 
amined by  a  drop  being  put  upon  a  slide,  as  in  some  cases 
very  light  diatoms  have  been  found  to  come  off  almost 
pure  in  one  or  more  of  these  earlier  washings.  The  quan- 
tity of  water  and  time  of  subsidence  given  may  be  taken 
generally,  but  may  require  to  be  modified  according  to 
circumstances  and  the  judgment  of  the  operator.  By  the 
repetition  and  variation  of  this  process — the  shaking  being 
the  most  important  part — the  gathering,  if  a  pure  one,  will 
be  sufficiently  clean.  If,  however,  it  contain  a  variety  of 
species  and  forms,  it  may  require  to  be  divided  into  different 
densities. 

In  some  cases,  however,  it  is  best  to  divide  the  gathering 
as  a  preliminary  operation,  which  may  be  done  by  agitating 
it  in  a  quantity  of  water  and  decanting  what  does  not 
readily  subside.  The  heavier  and  the  lighter  portions  are 
then  to  be  treated  as  two  separate  boilings.  But  when  the 
cleansing  has  been  carried  to  the  above  stage  and  this 
division  is  required,  the  plan  must  be  somewhat  as  follows  : — 
The  gathering  must  be  shaken  in  a  test-tube  with  six  inches 
of  water,  and  then  allowed  to  subside  until  one  inch  at  the 
top  remains  pure.  About  three  inches  are  then  to  be  care- 
fully withdrawn  by  a  pipette,  when  the  tube  may  be  filled 
up  and  the  operation  repeated.  The  three  lower  inches  also 
may  then  be  decanted  and  examined.  The  gathering  is 
thus  divided  into  three  portions ;  viz. — that  which  was 
withdrawn  by  the  pipette,  that  which  remained  floating 
in  the  lower  three  inches  of  water  in  the  tube,  and 
that  which  had  settled  at  the  bottom.  An  examination  of 
these  will  inform  the  operator  how  to  obtain  that  particular 
density  of  gathering  which  he  desires,  and  how  far  it  is 
worth  while  to  refine  this  process  of  elutriation ;  for  in 
cases  of  necessity  any  one,  or  all  three,  of  these  densities 
may  be  operated  upon  in  the  same  way  to  separate  a 
particular  diatom. 


OF   MICROSCOPIC   OBJECTS.  67 

As  an  occasional  aid,  it  may  be  remarked,  that  in  some 
cases  liquor  ammomc&  may  be  used  in  one  of  the  later 
washings  in  place  of  water,  as  it  often  separates  fine  dirt, 
which  is  not  otherwise  easily  removed.  Ammonia  also  dis- 
solves a  flocculent  matter  which  sometimes  remains;  and 
this  method  does  not  injure  diatoms  like  some  strong  alkalies. 
Some  fossil  deposits  require  to  be  treated  with  a  boiling 
solution  of  carbonate  of  soda  to  disintegrate  them ;  but 
this  operation  requires  great  care,  lest  the  alkali  should 
destroy  the  diatoms.  Vegetable  silicates  also  sometimes 
require  to  be  removed  by  a  solution  of  carbonate  of  soda ; 
but  as  the  frustules  of  the  diatoms  themselves  are  but 
vegetable  silica,  even  more  care  is  required  in  this  case.  It 
may  be  well  to  mention,  that  some  diatoms  are  so  imperfectly 
siliceous  that  they  will  not  bear  lotting  in  acid  at  all.  Some 
of  these  may  be  allowed  to  stand  in  cold  nitric  acid  some 
time,  whilst  others  of  a  smaller  and  more  delicate  character 
should,  when  possible,  be  treated  with  distilled  water 
alone. 

We  will  now  consider  the  mode  of  mounting  the  prepared 
diatoms,  which,  if  used  dry  (as  described  in  this  chapter), 
should  be  carefully  washed  two  or  three  times  with  the 
purest  distilled  water.  In  this  branch,  as  in  every  other, 
each  collector  gives  preference  to  that  method  in  which  he 
is  an  adept.  Thus  the  diatoms  may  be  placed  on  the 
under  side  of  the  cover,  to  be  as  near  to  the  object-glass 
as  possible,  or  upon  the  slide  itself;  and  each  plan  has 
its  advocates.  Whichsoever  of  these  is  used,  nothing  seems 
more  simple  to  the  novice  than  a  tolerably  equal  dispersion 
of  the  objects  upon  the  slide  or  cover;  but  this  is  by  no 
means  so  readily  accomplished ;  consequently  I  give  Mr. 
Rylands'  method,  as  his  slides  are  perfect  in  this  respect 
also.  He  always  places  the  diatoms  upon  the  thin  glass 
cover.  It  is  not  sufficient,  as  is  frequently  thought,  to 
take  a  drop  of  liquid  containing  the  cleansed  material  and 
spread  it  upon  the  cover  or  slide,  as  without  some  additional 
precaution  that  uniform  and  regular  distribution  of  the 
p  2 


68  PREPARATION   AND   MOUNTING 

specimens,  which  is  desirable,  is  not  obtained.  In  order  to 
effect  this,  let  a  drop  of  the  cleansed  gathering  be  diluted 
•sufficiently  for  the  purpose — how  much  must  be  determined 
in  each  case  by  experiment — and  let  the  covers  to  be 
mounted  be  cleaned  and  laid  upon  the  brass  plate.  (See 
•Chapter  II.)  By  means  of  a  glass  tube,  about  one-twelfth  of 
an  inch  in  diameter,  stopped  by  the  wetted  finger  at  the 
upper  end,  take  up  as  much  of  the  diluted  material  as  will 
form  a  moderately  convex  drop  extending  over  the  whole 
cover.  When  all  the  covers  required  are  thus  prepared, 
apply  a  lamp  below  the  brass  plate,  and  raise  the  tem- 
perature to  a  point  just  short  of  boiling.  By  this  means 
the  covers  will  be  dried  in  a  few  minutes,  and  the  specimens 
equally  distributed  over  the  whole  area.  The  spread  of 
the  fluid  upon  the  covers  is  facilitated  by  breathing  upon 
them  ;  and,  to  insure  uniformity,  care  must  be  taken  to 
avoid  shaking  them  whilst  drying.  The  best  plan  is  to 
mount  at  least  half  a  dozen  at  once. 

Before  mounting,  Mr.  Rylands  always  burns  the  diatoms 
upon  the  glass  at  a  dull  red  beat,  whether  they  are  used 
with  balsam  or  dry.  This  burning,  he  says,  is  not  only 
an  additional  cleaning  process,  but  it  effectually  fixes  the 
diatoms,  and  prevents  them  floating  out  if  mounted  with 
balsam.  The  thinnest  covers  may  be  burnt  without  damage 
if  they  are  placed  upon  a  small  piece  of  platinum  foil  of 
the  size  required,  which  should  be  about  one-hundredth  of 
an  inch  thick,  perfectly  flat,  and  having  three  of  its  edges 
slightly  bent  over,  so  as  to  prevent  its  warping  with  the 
heat.  The  small  flame  of  a  spirit-lamp,  or,  where  there  is 
gas,  a  Bunsen's  burner,  may  be  employed.  The  cover 
should  be  shaded  from  direct  daylight,  that  the  action  of 
the  flame  may  be  observed  more  perfectly.  Care  must  then 
be  taken  to  raise  the  temperature  only  to  the  dull  red  heat 
before  mentioned.  The  cover  will  then  be  in  a  fit  state  for 
mounting  as  required. 

It  has  been  stated  in  another  place  that  it  is  assumed 
that  the  operator  is  not  mounting  diatoms  simply  as  micros- 


OF   MICROSCOPIC   OBJECTS.  69 

copic  objects,  but  as  instructive  specimens.  It  is  not, 
therefore,  sufficient  to  take  a  single  slide  as  all  that  is 
required,  but  to  have  the  same  diatom  prepared  in  as  many 
ways  as  possible.  The  following  are  the  principal: — 

1.  Mounted  crude  in  fluid  (see  Chapter  "V.) 

2.  Burnt  crude  upon  the  cover,  and  mounted  dry  or  in 

balsam. 

3.  Mounted  dry  or  in  balsam  (see  Chapter  TV.),  after 

the  cleansing  process  already  described. 

I  will  here  give  Mr.  Ej lands'  method  of  mounting  them 
dry,  the  fluid  and  balsam  preparations  being  noticed  in 
their  respective  chapters.  The  slide,  with  the  ring  o£ 
asphalt,  or  black  varnish,  should  have  been  prepared  some 
weeks  previously,  in  order  to  allow  it  to  dry  thoroughly. 
When  required,  it  must  be  held  over  the  spirit-lamp  or 
Bunsen's  burner  until  the  ring  of  varnish  is  softened.  The 
burnt  cover,  having  been  heated  at  the  same  time,  must 
then  be  taken  in  the  forceps  and  pressed  upon  the  softened 
varnish  until  it  adhere  all  round.  When  cold,  an  outer 
ring  of  asphalt  completes  the  slide. 

Such  is  the  method  which  my  friend  Mr.  T.  G.  Rylands 
employs  in  the  preparation  of  diatoms  for  the  microscope. 
I  have  said  enough  concerning  his  results.  It  is  to  be 
feared,  however,  that  to  some  these  several  modes  of  opera- 
tion may  appear  lengthy  and  complicated  ;  but  if  read 
carefully,  and  the  experiments  tried,  they  will  be  found  to 
be  simple  enough  in  practice,  and  to  occupy  much  less  time 
than  an  intelligible  description  would  lead  the  novice  to 
believe  necessary, 

The  minute  nature  of  diatom  forms,  and  the  high  micros- 
copic powers  by  which  they  are  examined,  render  a  very 
shallow  cell  necessary  when  they  are  mounted  upon  a  dry 
slide.  Many  early  attempts,  on  this  account,  have  been 
ruined  by  the  cement  used  to  fix  the  thin  cover  spreading 
underneath.  A  correspondent  of  the  "  Monthly  Microscopic 
Journal "  thus  gives  his  mode  of  avoiding  this  : — "  There  is 
a  very  simple  means  of  avoiding  this  danger,  and  I  will 


70  PREPARATION   AND   MOUNTING 

now  describe  it.  A  circle  of  bitumen  about  one  third 
smaller  than  the  covering  glass  is  drawn  beforehand  on  my 
slides.  When  I  wish  to  make  a  preparation,  instead  of 
coating,  as  formerly,  the  first  circle  with  a  second  layer  of 
bitumen,  I  form  a  second  circle  of  it  outside  the  first,  and 
as  near  as  possible  to  it,  and  each  of  the  two  circles  has  its 
own  advantage ;  the  first,  in  fact,  while  forming  the  cell, 
serves  as  a  support  for  the  covering  glass,  and  thus  pre- 
serves the  Diatomacese  from  any  breakage;  it  offers,  besides, 
a  serious  obstacle  to  the  spreading  of  the  more  liquid  bitu- 
men of  which  the  outer  circle  is  composed ;  and  the  latter 
closes  the  cell  by  fixing  the  cover,  which,  when  the  prepara- 
tion is  dry,  may  be  covered  with  a  final  circle  of  bitumen. 
It  is  of  course  understood  that  I  am  speaking  of  prepara- 
tions made  in  the  dry  way  only,  and  not  with  balsam." 

One  of  the  most  fertile  as  well  as  the  most  curious  maga- 
zines of  Diatomacese  is  guano.  The  siliceous  forms  con- 
tained therein  have  been  devoured  by  sea-birds  and  passed 
through  the  stomach  uninjured,  and  after  lying  for  ages 
may  be  cleaned  and  classified.  Many  of  these  are  not  else- 
where met  with,  so  that  the  student  who  is  desirous  to  enter 
into  the  study  of  DiatomaceJB  must  be  instructed  as  to  the 
best  mode  of  obtaining  them  from  this  source.  The  par- 
ticulars to  be  observed  so  closely  resemble  those  before  men- 
tioned in  the  treatment  of  the  ordinary  diatoms,  that  it  will 
be  sufficiently  explicit  to  give  the  outlines  of  the  process. 
The  guano  must  be  first  washed  in  pure  water,  allowed  to 
subside  perfectly,  and  the  liquid  then  poured  off.  This 
must  be  repeated  until  the  top  fluid  is  clear,  and  care  taken 
not  to  decant  the  liquid  until  perfect  subsidence  has  taken 
place.  The  deposit  must  then  be  treated  with  hydrochloric 
acid  with  a  gentle  heat  for  an  hour  or  two,  adding  a  little 
fresh  acid  at  intervals  as  long  as  it  excites  any  effervescence. 
After  this  nitric  acid  must  be  substituted  for  the  hydro- 
chloric, and  the  heat  kept  up  to  almost  boiling-point  for 
another  hour  at  least,  adding  a  little  fresh  acid  as  before. 
When  this  ceases  to  act,  the  deposit  must  be  allowed  to 


OF   MICROSCOPIC   OBJECTS.  71 

settle  perfectly  and  the  acid  poured  off.  All  traces  of  the 
acid  must  now  be  washed  away  with  pure  water,  when  the 
remains  will  be  Diatomaceas,  the  sand  contained  in  the 
guano,  and  a  few  other  forms.  Some  of  these  may  be 
mounted  dry,  as  before  mentioned,  but  the  greater  portion 
should  be  put  up  in  Canada  balsam  as  described  in 
Chapter  IV. 

Such  is  the  ordinary  method  for  the  treatment  of  guano; 
but  Mr.  Rylands'  mode  of  proceeding  with  ordinary  Diato- 
maceas (before  given)  will  be  found  equally  successful  with 
these  deposits. 

The  composition,  however,  of  guano  is  more  complex  than 
the  substances  by  which  we  find  most  of  the  Diatomaceae 
surrounded,  and  therefore  a  different  method  of  treatment 
is  pursued  by  many.  The  following  by  Mr.  A.  J.  Roberts 
is  a  good  one  :  "  Guano  should  be  first  well  washed  with 
boiling  water,  either  on  a  paper  filter  or  by  repeated  affu- 
sions until  the  liquid  come  off  tasteless.  Boiling  water  is 
preferable  to  cold,  for  the  heat  expels  air-bubbles  and  causes 
the  deposit  to  settle  down  into  a  smaller  space ;  then  the 
deposit  must  be  subjected  to  the  action  of  the  acids  as 
directed  for  the  preparation  of  earths,  to  get  rid  of  the  lime 
salts.  The  partially  cleaned  deposit,  which  is  now  much 
smaller  in  bulk,  must  be  separated  as  much  as  possible 
from  the  liquid,  strong  sulphuric  acid,  in  sufficient  quantity 
to  cover  it,  poured  on  to  about  the  depth  of  half  an  inch, 
and  heat  applied  and  continued  for  sometime,  but  the  liquid 
must  not  be  made  to  boil.  The  result  will  be  an  almost  im- 
mediate blackening  of  the  liquid,  which  gradually  becomes 
deeper,  and  a  dirty,  inky-looking  compound  is  ultimately 
produced.  When  this  has  taken  place,  chlorate  of  potash 
in  fine  powder  must  be  dropped  into  the  hot  mixture  very 
gradually  until  the  black  colour  disappear.  Thia  must  be 
done  cautiously,  for  the  action  is  so  violent,  that  much 
spurting  is  occasioned  ;  and  the  liquid  being  very  corrosive, 
a  tolerably  capacious  vessel  should  be  used  in  order  to  keep 
the  splashes  within  reasonable  bounds,  or  serious  damage  to 


72  PREPARATION   AND   MOUNTING 

the  operator's  clothes  may  ensue.  The  nearly  decolorized 
liquid  must  now  be  diluted  with  a  considerable  quantity  of 
water,  and  the  deposit  allowed  to  subside,  the  supernatant 
liquid  poured  off,  and  the  process  of  heating  with  sulphuric 
acid  and  addition  of  chlorate  of  potash  repeated  until  the 
sulphuric  acid  occasion  no  further  blackening;  then  the 
cleaning  may  be  finished  in  the  usual  way  by  washing." 

I  have  had  many  complaints  from  my  friends  that  with 
all  their  care  they  have  found  nothing  fit  for  mounting  in 
guano.  This  is  readily  accounted  for  by  one  fact,  that  not 
one  sample  in  twenty  of  what  is  called  guano  in  the  market 
has  an  atom  of  guano  in  it.  Procure  real  guano,  and  you 
will  get  real  returns. 

The  fossil  Infusoria  (as  they  were  formerly  called)  are  now 
termed  Diatomacea3,  and  are  found  in  various  parts  of  the 
world  ;  such  as  Bermuda  earth,  Berg-mehl  from  Norway,  the 
deposit  from  Monrne  Mountain  in  Ireland,  &c.  They  are 
found  in  immense  quantities,  and  afford  the  microscopist 
innumerable  objects.  The  same  treatment  as  that  usually 
employed  for  the  Diatomacea3  must  be  followed  with  these 
deposits ;  but  as  they  are  sometimes  obtained  in  hard  masses, 
disintegration  is  first  necessary.  To  effect  this,  they  are 
usually  boiled  for  a  short  time  in  diluted  liquor  potasses, 
which  will  soon  cause  the  mass  to  fall  into  a  mud-like 
deposit.  Water  must  then  be  immediately  added,  in  order 
that  all  further  action  of  the  liquor  potasses  may  be  stopped, 
otherwise  the  objects  searched  for  will  be  dissolved.  For  this 
reason  it  is  necessary  to  understand  what  substance  is  being 
dealt  with,  because  some  deposits  are  much  finer  and  are 
acted  upon  more  readily  than  others. 

In  mounting  these  objeets,  some  are  so  delicate  that  they 
are  almost  invisible  when  balsam  is  used  with  them  ;  they 
are  therefore  usually  mounted  dry.  Others,  however,  are 
much  coarser,  and  may  be  mounted  in  balsam  like  the  Diato- 
macea?  mentioned  in  Chapter  IV. 

T^he  common  Infusoria  cannot  be  mounted  dry  with  any 
great  success,  though  a  few  may  be  placed  upon  the  glass 


OF    MICROSCOPIC    OBJECTS.  73 

slide  and  allowed  to  dry  naturally,  when  their  characters 
will  be  very  well  shown.  To  obtain  anything  like  a  natural 
appearance,  they  must  be  put  up  in.  fluid  as  in  Chapter  V. 

Next  to  the  Diatomacese,  no  class  of  microscopic  objects 
has  been  more  looked  into  of  late  than  the  Foraminifera. 
These  animals  are  almost  all  marine,  having  a  jelly-like  body 
enclosed  in  one  or  more  chambers  of  shell,  which  is  generally 
composed  of  carbonate  of  lime.  The  shells  are  made  with 
minute  orifices,  through  which  the  pseudopodia  (false  feet) 
are  extended  by  which  the  animal  is  enabled  to  lay  hold  of 
anything  to  draw  itself  along.  From  the  possession  of  these 
orifices  they  derive  their  name,  as  foramen  means  a  door  or 
opening.  They  have  been  found  in  every  depth  of  sea 
hitherto  sounded,  each  depth  being  abundant  in  certain 
species;  the  lowest  beds  containing  the  greatest  number  of 
specimens,  though  with  less  variation  of  kinds.  In  chalk 
they  are  found  in  a  fossil  state,  and  may  readily  be  shown 
(see  Chapter  IV.);  in  limestone  and  other  hard  stones  they 
are  abundant,  and  some  mountains  are  composed  principally 
of  these  shells. 

The  methods  of  obtaining  Foraminifera  are  various.  Many 
may  be  found  upon  seaweeds,  which  should  always  be  ex- 
amined as  soon  as  possible  after  gathering.  They  are  found 
in  masses  upon  some  coasts  where  the  waves  have  carried 
and  left  them  ;  but  they  are  to  be  found  the  most  abundantly 
in  sand  or  mud  dredged  from  the  bottom  of  the  sea.  They 
must,  however,  be  cleaned  and  separated  from  the  mass  of 
impurity  with  which  they  are  usually  mixed.  This  may  be 
done  in  various  ways,  according  to  the  nature  of  the  accom- 
panying matter.  If  sand  alone,  as  is  frequently  the  case, 
the  whole  mass  must  be  thoroughly  dried,  and  then  stirred 
up  in  clean  water.  The  sand  will  soon  subside  by  its  own 
weight,  but  the  chambers  of  the  Foraminifera,  being  filled 
with  air,  will  float  upon  the  surface,  and  may  be  skimmed 
off.  There  is,  however,  one  objection  to  this  mode  of  pro- 
ceeding— some  of  these  objects  are  so  minute,  the  chambers 
containing  comparatively  so  small  a  quantity  of  air,  that 


74  PREPARATION  AXV  MOUNTING 

they  sink  and  are  cast  away  with  the  refuse  sand.  On  this 
account  it  is  preferable  to  take  the  trouble  of  searching 
certain  soundings  under  the  microscope,  using  the  camel- 
hair  pencil,  or  some  other  contrivance  before  mentioned,  to 
extract  those  objects  which  are  required.*  To  clean  the 
Foraminifera,  Professor  Williamson  .advises  the  transfer  of 
the  specimens  to  an  evaporating  dish  containing  a  weak 
solution  of  caustic  potash.  This  must  be  boiled  for  some 
moments,  when  the  organic  matter  will  be  entirely  dissolved, 
and  the  calcareous  shells  left  free  from  impurity.  They 
must  now  be  well  washed  in  water,  so  that  all  alkaline 
matter  may  be  entirely  removed. 

If  the  specimens  are  in  mud,  we  must  proceed  in  a  dif- 
ferent way: — Stir  up  the  whole  mass  in  water,  and  allow 
it  to  stand  until  the  heavier  portion  has  sunk  to  the  bottom; 
the  water  may  then  be  poured  off  and  examined  to  see  if 
there- are  any  objects  contained  in  it.  This  process  must  be 
repeated  until  the  water  come  off  quite  clear,  when  (if  the 
search  is  for  Foraminifera  only)  the  solution  of  caustic 
potash  may  be  used  as  before  mentioned.  However  the 
soundings,  &c.,  are  cleaned,  it  is  necessary  to  assort  them 

*  In  searching  any  earth  or  sounding  in  order  to  take  objects  there- 
from, no  method  presents  the  same  facilities  as  the  use  of  (he  finest 
camel-hair  pencil,  to  which,  after  being  drawn  through  the  lips,  any 
forms  will  adhere,  and  yet  be  readily  detached  upon  the  slide.  After 
a  little  practice  the  smallest  objects  may  be  separated.  Captain  Lang, 
however,  stated  that  he  used  a  single  hair  or  bristle  dipped  into  gum 
and  dried,  after  which  a  slight,  breath  would  restore  its  adhesive 
power.  With  a  very  fine  hair  pencil  during  one  winter  I  mounted 
about  1,400  slides,  each  one  picked  out  of  sea  soundings,  many  of 
which  had  from  six  to  twelve  specimens  upon  them.  The  readiness 
with  which  the  objects  adhered  to  the  point  and  were  detached  when 
required,  rendered  the  process  much  more  pleasant  than  using  a  bristle 
with  gum.  As  to  the  numbers  qf  objects  to  be  taken  from  any  sound- 
ing, even  imagination  often  fails.  Plaucus,  it  is  said,  collected  6,000 
shells  of  Foraruinifera  from  an  ounce  of  sand  from  the  shore  of  the 
Adriatic.  Soldani  collected  from  less  than  an  ounce  and  a  half  of 
rock  from  the  hills  of  the  Casciana,  in  Tuscany,  10,454  fossil  shells. 
Several  of  these  were  so  minute  that  500  weighed  only  a  grain.  And 
D'Orbigny  found  3,840,000  specimens  in  an  ounce  of  saud  from  the 
shores  of  the  Antilles. 


or  MICROSCOPIC  OBJECTS.  75 

nnder  the  microscope  with  the  camel-hair  pencil  or  other 
contrivance,  as  it  is  impossible  to  obtain  them  fit  for  mount- 
ing without  undergoing  this  process. 

The  eea  soundings  taken  by  order  of  Government  are 
drawn  from  the  bottom  in  a  kind  of  apparatus  ingeniously 
made  for  the  purpose,  and  the  sand,  mud,  &c.,  are  brought 
up  in  their  original  state.  Common  soundings,  however, 
are  taken  by  lowering  a  heavy  piece  of  lead  coated  with 
tallow,  which  consequently  brings  up  a  small  portion  of  the 
matter  from  the  bottom.  Mr.  George  Mosley,  the  late 
Secretary  of  the  Manchester  Microscopic  Society,  obtained 
numbers  of  the  "scrapings"  from  the  sounding  leads.  To 
make  any  use  of  these  it  is,  of  course,  necessary  to  free  them, 
from  all  traces  of  the  tallow.  Mr.  Dancer  places  the  sound- 
ing in  a  basin  and  pours  boiling  water  upon  it,  which  causes 
the  melted  grease  to  rise  to  the  surface.  When  cold,  this 
may  be  removed,  and  the  water  carefully  decanted.  The 
operation  may  be  repeated  until  no  grease  appears,  when 
the  water  may  be  withdrawn  and  liquor  ammonias  used, 
which  will  form  a  soapy  solution  with  any  remaining  grease. 
This  must  be  treated  with  hot  water  for  the  final  washing. 
Care  must  be  taken  lest  the  finer  forms  be  carried  away  in 
decanting  the  washing  liquid.  Should  it  be  wished  to  make 
certain  as  to  this  point,  each  washing  should  be  examined 
under  the  microscope.  In  some  cases  the  process  of  Mr. 
Dancer  will  prove  sufficient.  Mr.  Dale,  however,  gives  a 
method  of  accomplishing  the  same  result,  which  is  much, 
more  readily  completed;  and  as  no  fault  can  be  found  with 
these  results,  I  will'here  give  it  in  full :  It  is  now  well  known 
that  one  of  the  products  obtained  from  the  naphtha  of  coal- 
tar  is  a  volatile,  oily  substance,  termed  benzole  (or,  by 
French  chemists,  benzine],  the  boiling-point  of  which,  when 
pure,  is  about  180°  Fahrenheit,  and  which  is  a  perfect 
solvent  of  fatty  substances.  In  a  capsule,  previously 
warmed  on  a  sand-bath,  Mr.  Dale  mixes  with  the  tallow 
soundings  some  of  this  benzole,  until  diluted  so  as  to  run 
freely,  pressing  the  lumps  with  a  glass  rod  until  thoroughly 


76  PREPABATION   AND   MOUNTING 

mingled  ;  the  solution  and  its  contents  are  then  poured  into 
a  paper  filter,  placed  in  a  glass  funnel ;  the  capsule  is  again 
washed  with  benzole,  until  the  whole  of  the  gritty  particles 
are  removed  into  the  filter.  A  washing-bottle  is  then  sup- 
plied with  benzole,  and  the  contents  of  the  filter  washed  to 
the  bottom  until  the  liquid  passes  off  pure,  which  may  be 
tested  by  placing  a  drop  from  the  point  of  the  funnel  on  a 
warm  slip  of  glass  or  bright  platinum,  when,  if  pure,  the 
benzole  will  evaporate  without  residue  or  tarnish ;  if  grease 
be  present,  the  washing  must  be  continued  until  they  are 
free  from  it.  After  rinsing  through  weak  acid,  -or  alcohol, 
for  final  purification,  the  calcareous  forms  will  be  ready  for 
mounting. 

The  filter  and  its  contents  may  be  left  to  dry  spontaneously, 
when  the  latter  can  be  examined  by  the  microscope.  Should 
time  be  an  object,  rapid  drying  may  be  effected  by  any  of 
the  usual  methods ;  one  of  which,  recommended  by  Mr. 
Dale,  is  to  blow  a  stream  of  hot  air  through  a  glass  tube 
held  in  the  flame  of  a  Bunsen's  burner.  The  lower  the 
boiling-point  of  the  benzole,  the  more  readily  can  the 
specimens  be  freed  from  it.  A  commoner  quality  may  be 
used,  but  it  is  more  difficult  to  dry  afterwards. 

Pare  benzole  being  costly,  this  may  appear  an  expensive 
process ;  but,  with  the  exception  of  a  trifling  loss  by 
evaporation,  the  whole  may  be  recovered  by  simple  dis- 
tillation. The  mixture  of  tallow  and  benzole  being  placed 
in  a  retort  in  a  hot-water,  a  steam,  or  a  sand  bath,  the 
benzole  will  pass  into  the  receiver,  and  the  tallow  or  other 
impurities  will  remain  in  the  retort.  When  the  whole  of 
the  benzole  has  distilled  over,  which  is  ascertained  by  its 
ceasing  to  drop  from  the  condenser,  the  heat  is  withdrawn 
and  the  retort  allowed  to  cool  before  the  addition  of  fresh 
material.  Half  a  dozen  to  a  dozen  filters,  each  with  its 
specimen,  can  be  in  process  at  the  same  time ;  and  the  dis- 
tillation of  the  recovered  benzole  progresses  as  quickly  as 
the  filtration,  which  was  practically  proved  on  the  occasion 
named.  The  process  is  very  dangerous  and  great  caution 


OF   MICROSCOPIC    OBJECTS.  77 

is  to  be  used  in  the  approach  of  light  to  the  inflammable 
vapour. 

After  the  Foraminifera  and  calcareous  forms  have  been 
removed,  the  residue  may  be  treated  with  acids  and  leviga- 
tion  in  the  usual  manner,  to  obtain  siliceous  forms  and 
discs,  if  there  be  any  present ;  but  to  facilitate  their 
deposition,  and  to  avoid  the  loss  of  any  minute  atoms 
suspended  in  the  washings,  I  would  suggest  the  use  of 
filtration.  The  conical  filter  is  unsuitable,  as  the  particles 
would  spread  over  too  great  a  surface  of  paper ;  but  glass 
tubes  open  at  both  ends  (such  as  broken  test-tubes)  will  be 
found  to  answer,  the  broad  end  covered  with  filtering-paper 
and  over  that  a  slip  of  muslin  tied  on  with  a  thread  to 
facilitate  the  passage  of  the  water  and  prevent  the  risk  of 
breaking  the  paper.  Suspend  the  tube  over  a  suitable 
vessel  through  a  hole  cut  in  thin  wood  or  cardboard,  pour 
in  the  washings,  which  can  be  thus  filtered  and  then  dried. 
The  cloth  must  be  carefully  removed,  the  paper  cut  round 
the  edges  of  the  tube,  and  the  diatoms  on  the  paper  disc 
may  be  removed  by  a  camel-hair  pencil  or  otherwise,  ready 
for  mounting.  Thus  many  objects  may  be  preserved  which 
would  be  either  washed  away  or  only  be  obtained  by  a  more 
tedious  process. 

Such  is  Mr.  Dale's  method  of  cleaning  the  soundings 
from  tallow,  and  as  it  thoroughly  accomplishes  its  end,  and 
is  alike  effective  and  not  injurious  to  Foraminifera  and  dia- 
toms, it  may  be  safely  recommended.  The  weak  solution  of 
caustic  potash  before  advised  for  Foraminifera,  must  not  be 
used  where  it  is  desired  to  preserve  the  diatoms,  as  they 
would  certainly  be  injured,  or  destroyed  altogether,  if  this 
agent  were  employed. 

In  fixing  the  Foraminifera  upon  the  slide,  no  better  plan 
can  be  followed  than  the  dry  cells  and  gum  recommended 
in  the  early  parts  of  this  chapter.  Owing  to  their. thickness 
and  composition,  most  of  them  are  opaque  objects  only;  but 
they  are  exquisitely  beautiful,  and  require  no  particular  care, 
except  in  allowing  the  cell  to  be  perfectly  dry  when 


78  PREPARATION  AND  MOUNTING 

the  cover  is  placed  upon  it,  or  the  damp  will  certainly 
become  condensed  upon  the  inner  side,  and  the  examination 
seriously  hindered. 

Many  of  the  Foraminifera  require  cutting  into  sections  if 
it  is  wished  to  examine  their  internal  structure  ; — "  decal- 
cifying "  is  also  desirable  in  some  cases :  both  of  these 
processes  will  be  found  described  at  length  in  the  chapter  on 
Sections  and  Dissections. 

When  more  than  one  specimen  of  some  particular  shell  is 
obtained,  it  is  better  to  place  them  upon  the  slide  in  dif- 
ferent positions,  so  as  to  show  as  much  of  the  structure  as 
possible.  I  will  conclude  this  subject  by  quoting  a  passage 
from  T.  Eymer  Jones :  "  It  is,  therefore,  by  no  means  suf- 
ficient to  treat  these  shells  as  ordinary  objects  by  simply 
laying  them  on  a  glass  slide,  so  as  to  see  them  only  from 
one  or  two  points  of  view ;  they  must  be  carefully  examined 
in  every  direction,  for  such  is  the  diversity  of  form  that 
nothing  short  of  this  will  be  at  all  satisfactory.  For  this 
purpose,  they  should  be  attached  to  the  point  of  a  fine 
needle,  so  that  they  may  be  turned  in  any  direction,  and 
examined  by  reflected  light  condensed  upon  them  by  means 
of  a  lens  or  side  reflector.  In  many  of  the  thick-shelled 
species  it  will  be  necessary  to  grind  them  down  on  a  hone 
[see  Chapter  VI.]  before  the  number  and  arrangement  of 
the  internal  chambers  is  discernible ;  and  in  order  to 
investigate  satisfactorily  the  minutiaa  of  their  structure, 
a  variety  of  sections,  made  in  various  ways,  is  indis- 
pensable." 

A  visitor  to  the  seaside  may  with  little  trouble  procure 
one  of  the  most  beautiful  objects  which  can  ornament  a 
cabinet.  On  turning  over  stones  which  have  been  covered 
by  the  last  tide,  a  very  small  species  of  starfish  will  often  be 
met  with.  From  a  small  circular  centre  five  long  arms 
project,  each  of  which  is  covered  with  spines  beautifully 
arranged.  When  found,  they  should  be  dropped  into  fresh 
water  with  a  little  spirit  added.  This  kills  them  instantly, 
else  many  of  their  long  arms  get  broken  by  their  struggles. 


OF   MICROSCOPIC   OBJECTS.  79 

By  putting  them  into  water  the  arms  are  rendered,  soft  and 
may  then  be  spread  in  forms  best  suited  to  microscopic 
slides,  and  thus  allowed  to  dry.  They  are  beautifully 
delicate  in  colour,  needing  no  preparation  to  bleach  them. 
During  one  morning's  walk  at  Llandudno  I  procured  about 
three  dozen. 

Plants  afford  an  almost  inexhaustible  treasury  for  the 
microscope,  and  many  of  them  show  their  beauties  best  when 
mounted  dry.  When  any  of  these  are  to  be  mounted,  care 
must  be  taken  that  they  are  thoroughly  dry,  otherwise  the 
damp  will  certainly  arise  in  the  cell,  and  injure  the  object; 
and  it  may  here  be  mentioned  that  long  alter  a  leaf  has 
every  appearance  of  dryness,  the  interior  is  still  damp,  and 
no  way  can  be  recommended  of  getting  rid  of  this  by  any 
quicker  process  than  that  of  keeping  them  in  a  warm  room, 
as  many  leaves,  &c.,  are  utterly  spoiled  by  using  a  hot  iron 
or  other  contrivance.  The  safest  way  is  to  press  them 
gently  betwixt  blotting-paper,  which  may  be  removed  and 
dried  at  short  intervals ;  and  though  this  may  appear  a 
tedious  operation,  it  is  a  safe  one. 

On  the  surface  of  leaves,  hairs  and  scales  of  various  and 
very  beautiful  forms  are  found,  most  of  which  display  their 
beauties  best  when  removed  from  the  leaf,  and  used  with 
the  polarizer.  These  will  be  noticed  in  another  place ;  but 
a  portion  of  the  leaf  should  always  be  prepared  in  its  natural 
form,  to  show  the  arrangement  of  the  hair  or  scales  upon  it; 
and  this  must  almost  invariably  be  mounted  dry  when  used 
for  this  purpose.  Many  of  them  require  very  delicate 
handling.  The  epidermis,  or,  as  it  is  by  some  termed,  the 
cuticle,  is  the  outer  skin  which  lies  upon  the  surface  of  the 
leaves  and  other  parts  of  most  plants.  This  is  composed  of 
cells  closely  connected,  often  bearing  the  appearance  of  a 
rude  network.  In  many  plants,  by  scraping  up  the  surface 
of  the  leaf,  a  thin  coating  is  detached,  which  may  be  torn 
off  by  taking  hold  of  it  with  forceps.  The  piece  may  then 
be  washed  and  floated  upon  a  glass  slide,  where,  on  dry- 
ing, it  will  be  firmly  fixed,  and  may  usually  be  mounted 


80  PREPARATION  AND   MOUNTING 

dry.  Amongst  the  most  beautiful  and  easily  prepared  of 
these  may  be  mentioned  the  petal  of  the  geranium,  the 
cells  of  which  are  well  denned  and  amongst  the  most 
interesting. 

Sometimes  this  cuticle  is  removed  by  maceration  of  the 
leaf  in  water  or  by  a  quicker  method — boiling  in  nitric  acid. 
Perhaps  it  will  be  as  well  to  give  Mr.  Arnold's  experience. 
"  A  leaf  of  a  rhododendron  which  had  been  dry  some 
months,  and  a  freshly-gathered  leaf  of  an  azalea,  were  put  into 
a  test-tube,  and  covered  with  undiluted  nitric  acid  of  com- 
merce of,  I  believe,  about  T32  specific  gravity ;  the  tube  was 
held  over  a  spirit-lamp  until  the  acid  just  boiled,  and 
the  contents  were  then  thrown  into  a  basin  of  cold  water. 
The  cuticle  of  the  rhododendron  leaf  partially  separated 
spontaneously ;  that  of  the  azalea  came  off  without  the 
least  difficulty.  The  whole  operation  did  not  occupy  moi'e 
than  five  minutes.  Undoubtedly  many  leaves,  according  to 
their  texture,  will  require  different  strengths  of  acid,  and 
longer  or  shorter  periods  of  boiling." 

Closely  connected  with  the  leaves  are  the  ANTHERS  and 
POLLEN,  of  which  a  great  number  are  beautiful  and  interesting 
subjects  for  the  microscopist. 

The  mallow  tribe  will  furnish  some  exquisite  objects, 
bearing  the  appearance  of  masses  of  costly  jewels.  These 
are  usually  dried  with  pressure,  but  the  natural  form  may 
be  more  accurately  preserved  by  allowing  them  to  dry  as 
they  are  taken  from  the  flower,  with  no  interference  except 
thoroughly  protecting  them  from  all  dust.  Sometimes  the 
anther  is  divided,  so  that  the  cell  required  to  receive  them 
may  be  of  as  little  depth  as  possible.  The  common  mallow 
is  a  beautiful  object,  but  I  think  the  lavatera  is  a  better,  as 
it  shows  the  pollen-chambers  well,  when  dried  unpressed. 
The  pollen  is  often  set  alone,  and  is  well  worth  the  trouble, 
as  it  then  admits  of  more  close  examination.  Often  it  is 
convenient  to  have  the  anther  and  pollen  as  seen  in  nature 
on  one  slide,  and  the  pollen  alone  upon  another.  The 
former  should  be  taken  from  the  flowers  before  their  full 


OF   MICROSCOPIC   OBJECTS.  81 

development  is  attained,  as,  if  overgrown,  they  lose  much  of 
their  beauty.  Some  pollens  are  naturally  so  dark  that  it  is 
necessary  to  mount  them  in  Canada  balsam  or  fluid,  as 
described  in  other  places ;  but  they  are  better  mounted  dry 
when  they  are  not  too  opaque. 

Here  we  may  also  mention  the  SEEDS  of  many  plants  as 
most  interesting,  and  some  of  them  very  beautiful,  objects, 
requiring  for  the  greater  part  but  a  low  power  to  show  them. 
Most  of  these  are  to  be  mounted  dry,  as  opaque  objects,  in 
cells  suited  to  them,  but  some  are  best  seen  in  balsam,  and 
will  be  mentioned  in  Chapter  IV. 

The  CORALLINES,  many  of  which  are  found  on  almost  every 
coast,  afford  some  very  valuable  objects  for  the  microscope. 
They  must  be  well  washed  when  first  procured,  to  get  rid  of 
all  the  salts  of  the  sea-water,  dried  and  mounted  in  cells 
deep  enough  to  protect  them  from  all  danger  of  pressure, 
as  some  of  them  are  exceedingly  fragile.  The  white  ivory 
appearance  which  some  of  them  present  is  given  to  them  by 
an  even  covering  of  carbonate  of  lime ;  and  should  it  be 
desired  to  examine  the  structure  of  these  more  closely,  it 
may  be  accomplished  by  keeping  them  for  some  time  in 
vinegar  or  dilute  muriatic  acid,  which  will  remove  the  lime 
and  allow  of  the  substance  being  sliced  in  the  same  way  as 
other  Alga3.  ("  Micrographic  Dictionary,"  p.  183.) 

THE  SCALES  OF  INSECTS. — The  fine  dust  upon  the  wings 
of  moths  and  butterflies,  which  is  so  readily  removed  when 
they  are  handled  carelessly,  is  what  is  called  the  scales.  To 
these  the  wing  owes  the  magnificent  colours  which  so  often 
are  seen  upon  it ;  every  particle  being  what  may  be  termed  a 
distinct  flat  feather.  How  these  are  placed  (somewhat  like 
tiles  upon  a  roof)  may  be  easily  seen  in  the  wing  of  any 
butterfly,  a  few  being  removed  to  aid  the  investigation. 
Their  form  is  usually  that  of  the  battledore  with  which 
the  common  game  is  played,  but  the  handle  or  base  of  the 
scale  is  often  short,  and  the  broad  part  varies  in  propor- 
tionate length  and  breadth  in  different  specimens.  The 
markings  upon  these  also  vary,  some  being  mostly  composed 


82  PREPARATION  AND   MOUNTING 

of  lines  running  from  the  base  to  the  apex,  others  reminding 
us  of  network — bead-like  spots  only  are  seen  in  some — • 
indeed,  almost  endless  changes  are  found  amongst  them. 
These  scales  are  not  confined  to  butterflies  and  moths,  nor 
indeed  to  the  icings  of  insects.  The  different  gnats  supply 
eome  most  beautiful  specimens,  not  only  from  the  wings, 
but  also  from  the  proboscis,  &c. ;  whilst  from  still  more 
minute  insects,  as  the  podura,  scales  are  taken  which  are 
esteemed  as  a  most  delicate  test.  The  gorgeous  colours 
which  the  diamond  beetles  ehow  when  under  the  microscope 
are  produced  by  light  reflected  from  minute  scales  with 
which  the  insects  are  covered. 

In  mounting  these  objects  for  the  microscope  it  is  well  to 
have  the  part  of  the  insect  from  which  the  scales  are  usually 
taken  as  a  separate  slide,  so  that  the  natural  arrangement 
of  them  may  be  seen.  This  is  easily  accomplished  with  the 
wings  of  butterflies,  gnats,  &c. ;  as  they  require  no  extra- 
ordinary care.  In  mounting  the  scales  they  may  be  placed 
upon  slides,  by  passing  the  wings  over  the  surface,  or  by 
gently  scraping  the  wing  upon  the  slide,  when  they  must  be 
covered  with  the  thin  glass.  Of  course,  the  extreme  tenuity 
of  these  objects  does  away  with  the  necessity  of  any  cell 
excepting  that  formed  by  the  gold-size  or  other  cement  used 
to  attach  the  cover.  The  scales  of  the  podura  should  be 
placed  upon  the  slide  in  a  somewhat  different  manner.  This 
insect  is  without  wings,  and  is  no  longer  than  the  common 
flea.  It  is  often  found  amongst  the  sawdust  in  wine-cellars, 
continually  leaping  about  by  the  aid  of  its  tail,  which  is 
bent  underneath  its  body.  Dr.  Carpenter  says  : — "  Podura 
may  be  obtained  by  sprinkling  a  little  oatmeal  on  a  piece 
of  black  paper  near  their  haunts ;  and  after  leaving  it  there 
for  a  few  hours,  removing  it  carefully  to  a  large  glazed  basin, 
BO  that,  when  they  leap  from  the  paper  (as  they  will  when 
brought  to  the  light),  they  may  fall  into  the  basin,  and  may 
thus  separate  themselves  from  the  meal.  The  best  way  of 
obtaining  their  scales,  is  to  confine  several  of  them  together 
beneath  a  wine-glass  inverted  upon  a  piece  of  fine  smooth 


OF  MICROSCOPIC   OBJECTS.  83 

paper;  for  the  scales  will  become  detached  by  their  leaps 
against  the  glass,  and  will  fall  upon  the  paper."  These 
scales  are  removed  to  the  slide,  and  mounted  as  those  from 
gnats,  &c.  When  the  podura  has  been  caught  without  the 
aid  of  meal,  it  may  be  placed  upon  the  slide,  under  a  test- 
tube,  or  by  any  other  mode  of  confinement,  and  thus  save 
the  trouble  of  transfer  from  the  paper  before  mentioned. 
Another  method  is  to  seize  the  insect  by  the  leg  with  the 
forceps  and  drag  it  across  the  slide,  when  a  sufficient  quan- 
tity of  scales  will  probably  be  left  upon  it. 

Mr.  Mclntyre  procures  the  scales  in  the  following  man- 
ner : — He  makes  what  he  terms  a  breeding-cage,  by  taking 
a  piece  of  plate-glass  four  inches  long  by  two  inches  wide, 
and  over  this  places  a  few  sheets  of  blotting-paper.  Upon 
these  he  lays  a  sheet  of  cork  about  a  quarter  of  an  inch 
thick,  with  a  circle  cut  out  of  the  centre  one  inch  wide. 
This  gives  a  kind  of  box,  which  he  covers  with  glass,  kept 
firm  by  two  elastic  bands.  He  says  : — "  After  capturing 
the  insect  by  means  of  a  tube  and  a  camel-hair  pencil,  I  let 
it  remain  for  some  days  in  one  of  the  breeding-cages,  into 
which  I  always  transfer  the  newly-caught  podura,  until  it 
has  changed  its  skin  ;  then  I  stupefy  it  with  chloroform, 
and  drop  it  out  on  to  a  thin  glass  cover  (previously  cleaned) 
and  with  a  very  clean  needle-point  roll  it  backwards  and 
forwards  upon  the  cover  till  sufficient  scales  are  removed. 
A  very  light  pressure  is  indispensable,  so  as  not  to  squeeze 
out  any  of  the  insect's  fluids." 

These  scales  are  usually  mounted  dry ;  but  Hogg  re- 
commends the  use  of  Canada  balsam  (Chapter  IV.)  as  ren- 
dering their  structure  more  definite  when  illuminated  with 
Wenham's  parabolic  reflector.  Some  advise  other  methods, 
which  will  be  mentioned  in  Chapter  V.  As  most  insects 
when  undissected  are  mounted  in  Canada  balsam,  the  dif- 
ferent modes  of  treatment  which  they  require  will  be  stated 
in  another  place. 

In  mounting  blood  of  any  kind  to  show  the  corpuscles, 
or,  as  they  are  often  called,  globules,  which  are  round  or 

o2 


8i  PREPARATION  AND   MOUNTING 

oval  discs,  it  is  bat  necessary  to  cover  the  slide  on  the  spot 
required  with  a  coating  as  thin  as  possible  and  allow  it  to 
dry  before  covering  with  thin  glass.  There  is  a  slight  con- 
traction in  the  globules  when  dried,  but  not  enough  to  in- 
jure them  for  the  microscope.  The  shape  of  these  varies  in 
different  classes  of  animals,  but  the  size  varies  much  more, 
some  being  many  times  larger  than  others.  Perhaps  it  will 
not  be  out  of  place  to  say  a  few  words  concerning  the  detec- 
tion of  blood.  Wherever  the  stains  are,  they  must  be  care- 
fully scraped  away  and  immersed  for  a  few  hours  in  a  weak 
solution  of  bichloride  of  mercury.  With  a  thin  tube  the 
more  solid  portion  may  then  be  removed  to  a  glass  slide  and 
examined  with  a  somewhat  high  power.  A  slight  knowledge 
of  the  microscopic  appearance  of  blood-discs  will  show  us 
•whether  the  suspicion  of  blood  is  correct. 

Some  of  the  skins  of  larvae,  are  beautiful  objects ;  but,  like 
many  sections  of  animal  and  other  fragile  matter,  are  diffi- 
cult to  extend  upon  the  slide.  This  difficulty  is  easily  over- 
come by  floating  the  thin  object  in  clear  water,  immersing 
the  slide,  and  when  the  object  is  evenly  spread  gently  lifting 
it.  Allow  it  then  to  dry  by  slightly  raising  one  end  of 
the  slide  to  aid  the  drainage,  and  cover  with  thin  glass  as 
other  objects.  The  tails  and  fins  of  many  small  fish  may 
be  mounted  in  a  similar  manner,  and  are  well  worth  the 
trouble. 

A  few  objects  which  are  best  shown  by  mounting  dry 
may  be  here  mentioned  as  a  slight  guide  to  the  beginner, 
though  some  of  them  have  been  before  noticed.  Many  of 
the  Foraminifera,  as  elsewhere  described.  Some  crystals  are 
soluble  in  almost  any  fluid  or  balsam,  and  should  be  mounted 
dry;  a  few,  however,  deliquesce  or  effloresce,  which  renders 
them  worthless  as  microscopic  objects. 

The  wings  of  butterflies,  gnats,  and  moths  will  afford 
many  specimens  wherewith  to  supply  the  cabinet  of  the 
young  student.  A  great  variety  of  scales  also  may  be  found 
amongst  the  ferns;  indeed,  these  alone  will  afford  the 
student  occupation  for  a  long  time.  On  the  under-side  of 


OF   JllCiiOSCOPIC   OBJECTS.  85 

the  leaves  are  the  reservoirs  for  the  spores,  which  in  many 
instances  somewhat  resemble  green  velvet,  and  are  arranged 
in  stripes,  round  masses,  and  other  forms.  The  spores  are 
usually  covered  with  a  thin  skin,  which  is  curiously  marked 
in  some  specimens,  often  very  like  pollen-grains.  The  man- 
ner in  which  these  spores  with  all  their  accompaniments 
are  arranged,  their  changes  and  developments,  afford  almost 
endless  subjects  for  study;  different  ferns  presenting  us  with 
many  variations  in  this  respect  totally  invisible  without  the 
aid  of  the  microscope.  The  hymenophyllums  (of  which  two 
only  belong  to  England)  are  particularly  interesting,  and 
the  structure  of  the  leaves  when  dried  makes  them  beautiful 
objects,  often  requiring  no  balsam  to  aid  their  transparency. 
Portions  of  the  fronds  of  ferns  should  be  mounted  as  opaque 
objects,  after  having  been  dried  between  blotting-paper, 
when  they  are  not  injured  by  pressure;  but  care  must  be 
taken  to  gather  them  at  the  right  time,  as  they  do  not  show 
their  beauty  before  they  are  ripe,  and  if  over-ripe  the  ar- 
rangement of  the  spores,  &c.,  is  altered.  The  spores  may 
be  mounted  as  separate  objects  in  the  same  manner  as 
pollen,  before  mentioned,  and  are  exquisitely  beautiful  when 
viewed  with  a  tolerably  high  power.  The  number  of  foreign 
ferns  now  cultivated  in  this  country  has  greatly  widened 
the  field  for  research  in  this  direction  ;  and  it  may  also  be 
mentioned  that  the  under-sides  of  many  are  found  to  be 
covered  with  scales  of  very  beautiful  forms.  A  small 
piece  of  the  frond  of  one  of  these  may  be  mounted  in  its 
natural  state,  but  the  removal  of  the  scales  for  examina- 
tion by  polarized  light  will  be  described  in  another  place. 
The  mosses  also  are  quite  a  little  world,  requiring  but  a  low 
power  to  show  their  beauties.  The  leaves  are  of  various 
forms,  some  of  which  resemble  beautiful  net-work ;  the 
"  urns  "  or  reservoirs  for  the  spores,  however,  are  perhaps 
the  most  interesting  parts  of  these  objects,  as  also  of  the 
liverworts  which  are  closely  allied  to  the  mosses.  These 
urns  are  generally  covered  by  lids,  which  fall  off  when 
the  fruit  is  ripe.  At  this  period  they  are  well  fitted  for  the 


86  PKEPAEATION  AKD  MOUNTING 

microscope.  The  common  screw-moss  may  be  found  in 
great  abundance,  and  shows  this  denudation  of  the  spores 
very  perfectly.  Many  of  these  may  be  easily  dried  without 
much  injury,  but  they  should  also  be  examined  in  their 
natural  state. 

The  student  should  not  omit  from  his  cabinet  a  leaf  of 
the  nettle  and  the  allied  foreign  species,  the  mystery  ot 
which  the  microscope  will  make  plain.  The  hairs  or  stings 
may  also  be  removed,  and  viewed  with  a  higher  power  than 
when  on  the  leaf,  being  so  transparent  as  to  require  no  bal- 
sam or  other  preservative. 

There  are  few  more  interesting  objects  than  the  rapliides 
or  plant-crystals.  These  are  far  from  being  rare,  but  in 
Borne  plants  they  are  very  minute,  and  consequently  require 
care  in  the  mounting,  as  well  as  a  high  magnifying  power 
to  render  them  visible ;  in  others  they  are  so  large  that 
about  twenty -five  of  them  placed  point  to  point  would  reach 
one  inch.  Some  of  these  crystals  are  long  and  compara- 
tively very  thin,  which  suggested  the  name  (rapliis,  a 
needle) ;  others  are  star-like,  with  long  and  slender  rays ; 
while  others  again  are  of  a  somewhat  similar  form,  each  ray 
being  solid  and  short.  If  the  stem  of  rhubarb,  or  almost 
any  of  the  hyacinth  tribe,  be  bruised,  so  that  the  juice  may 
flow  upon  the  slide,  in  all  probability  some  of  these  crys- 
tals will  be  found  in  the  fluid.  To  obtain  them  clean, 
they  must  be  freed  from  all  vegetable  matter  by  maceration. 
After  this  they  must  be  thoroughly  washed  and  mounted 
dry.  They  are  also  good  polarizing  objects,  giving  bril- 
liant colours ;  but  when  used  for  this  purpose  they  must 
be  mounted  as  described  in  Chapter  IV.  A  few  plants 
which  contain  them  may  be  mentioned  here.  The  Cac- 
tacese  are  very  prolific ;  the  orchids,  geraniums,  tulips,  and 
the  outer  coating  of  the  onion,  furnish  the  more  unusual 
forms. 

The  Fungi  are  generally  looked  upon  as  a  very  difficult 
class  of  objects  to  deal  with,  but  amongst  them  some  of 
the  most  available  may  be  found.  The  forms  of  many  are 


OP   MICROSCOPIC   OBJECTS.  87 

very  beautiful,  but  are  so  minute  as  to  require  a  high  mag- 
nifying power  to  show  them.  The  mould  which  forma  on 
many  substances  is  a  fungus,  and  in  some  cases  may  be 
dried  and  preserved  in  its  natural  state.  A  friend  of  mine 
brought  me  a  rose-bush  completely  covered  with  a  white 
blight.  This  was  found  to  be  a  fungus,  which  required  a 
high  magnifying  power  to  show  it.  Being  a  very  interesting 
object,  it  was  desirable  to  preserve  it,  and  this  was  perfectly 
effected  without  injury  to  the  form  by  simply  drying  the 
leaf  in  a  room  usually  occupied.  Amongst  the  fungi  are 
many  objects  well  worth  looking  for,  one  of  which  is  the 
Diaclicea  elegans.  This,  the  only  species,  says  the  Micro- 
graphic  Dictionary,  is  found  in  England  upon  the  living 
leaves  of  the  lily-of-the-valley,  &c.  These  little  plants  grow 
in  masses,  reminding  one  of  mould,  to  a  height  of  a  quarter 
of  an  inch,  and  each  "  stem  "  is  covered  with  a  sheath,  in 
shape  somewhat  like  an  elongated  thimble.  When  ripe  the 
sheath  falls  off  and  reveals  the  same  shaped  column,  made 
up  of  beautifully  fine  network,  with  the  spores  lying  here  and 
there.  This  dries  well,  and  is  a  good  object  for  the  middle 
powers.  Amongst  the  fungi  the  blights  of  wheat  and  of 
other  articles  of  food  may  be  included.  Many  of  them  may 
be  mounted  dry ;  others,  however,  cannot  be  well  pre- 
served except  in  liquids,  and  will  be  referred  to  in  Chap- 
ter V.  When  rambling  in  a  wood  during  the  summer  I  sat 
down  upon  the  fallen  trunk  of  a  tree,  and  here  and  there  a 
few  minute  white  spots  caught  my  eye.  I  took  my  Cod- 
dington  lens  from  my  side-pocket  and  applied  it  to  these. 
Judge  of  my  surprise  when  I  found  each  white  speck  a 
distinctly  formed  fungus  resembling  in  size  and  form,  to  an 
amusing  similarity,  a  disc  of  the  arachnoidiscus.  They  were 
already  dry,  and  I  mounted  them  as  ordinary  dry  objects ; 
and  hitherto  no  change  has  taken  place  which  I  can  detect. 
Amongst  the  zoophytes  and  sea-mats,  commonly  called 
sea-weeds,  may  be  found  very  many  interesting  objects  to 
be  mounted  dry.  When  this  mode  of  preservation  is  used, 
it  is  necessary  that  all  the  sea-salt  be  thoroughly  washed 


SB  PREPARATION   AND   MOUNTING 

from  them.  As  they  are,  however,  most  frequently  mounted 
in  balsam  or  liquid,  they  will  be  more  fully  noticed  in  other 
places. 

The  scales  of  fishes  are  generally  mounted  dry  when 
used  as  ordinary  objects ;  but  for  polarized  light,  balsam  or 
liquid  must  be  used,  as  noticed  in  Chapter  IV.  To  mount 
a  fish-scale,  however,  in  a  satisfactory  manner,  care  must  be 
taken  that  it  is  perfectly  clean.  This  can  be  accomplished 
only  by  careful  washing,  in  which  process  soft  camel-hair 
pencils  will  often  be  useful.  When  the  slime  or  mucus  haa 
once  dried,  it  is  very  difficult  to  remove.  The  variety  and 
beauty  of  these  are  quite  surprising  to  the  novice.  It  is 
also  very  interesting  to  procure  the  skin  of  the  fish  when 
possible,  and  mount  it  on  a  separate  slide  to  show  how  the 
scales  are  arranged.  The  sole  ia  one  of  the  most  unusual 
forms,  the  projecting  end  of  each  scale  being  covered  with 
spines,  which  radiate  from  a  common  centre,  while  those  at 
the  extremity  are  carried  out  somewhat  resembling  the  rays 
of  a  star.  One  of  the  skates  has  a  spine  projecting  from  the 
centre  of  each  scale,  which  is  a  very  curious  opaque  object, 
especially  when  the  skin  is  mounted  in  the  manner  described. 
The  perch,  roach,  minnow,  and  others  of  the  common  fishes 
give  the  student  good  objects  for  his  cabinet,  and  may  be 
procured  without  difficulty.  The  scale  of  the  turbot  is  a 
splendid  object  for  the  polariscope  when  mounted  in  balsam. 

Insects  which  are  very  transparent,  or  have  the  "  metallic 
lustre"  with  which  any  medium  would  interfere,  are  mounted 
dry.  The  diamond-beetle,  before  mentioned,  is  a  splendid 
example  of  this ;  the  back  is  generally  used,  but  the  legs, 
showing  the  curious  feet,  are  very  interesting  objects.  In- 
deed, amongst  the  legs  and  feet  of  insects  there  is  a  wide 
field  of  interest.  When  they  are  of  a  horny  nature,  it  is 
best  to  dry  them  in  any  form  preferred,  but  to  use  no 
pressure;  when,  however,  they  are  wanted  flat,  so  as  to 
show  the  feet,  &c.,  extended,  they  must  be  dried  with  a 
gentle  pressure  betwixt  blotting-paper  if  possible.  But  this 
will  be  treated  more  fully  in  Chapter  IV. 


OF  MICROSCOPIC   OBJECTS.  89 

The  eyes  of  insects  are  sometimes  allowed  to  dry  in  their 
natural  shape,  and  mounted  as  opaque  objects;  but  generally 
they  are  used  as  transparencies  in  balsam  or  liquid,  so  the 
description  of  the  treatment  which  they  require  will  be 
deferred  to  Chapter  IV. 

Hairs,  when  not  too  dark,  are  sometimes  transparent 
enough  when  mounted  dry,  but  are  usually  mounted  in 
balsam.  These  will  be  more  fully  noticed  in  another  place, 
but  there  are  some  without  which  no  cabinet  is  deemed  in 
anywise  complete.  Many  different  species  of  bats,  English 
and  foreign,  present  us  with  hairs  the  form  of  which  we 
should  never  have  dared  to  imagine  without  microscopic 
aid.  Other  curious  objects  are  found  in  the  antennae 
of  crabs.  You  can  also  readily  know  whether  you  are  being 
deceived  when  you  buy  what  yon  deem  a  real  sealskin  or 
sable.  From  some  of  the  common  caterpillars  I  have  ob- 
tained exquisitely  beautiful  slides,  and  a  kangaroo  is  a  true 
friend  to  an  object-gatherer. 

The  hair  of  the  ornithorhynchus  is  a  very  curious  object, 
having  a  thin  place  in  the  middle  of  its  length,  and  so  pre- 
senting somewhat  the  appearance  of  a  flail. 

These  are  a  few  of  the  objects  which  are  often  mounted 
dry,  but  some  of  them  should  be  shown  in  balsam  or  liquid 
also,  and  there  is  much  difference  of  opinion  as  to  the  best 
way  of  preserving  others.  This,  however,  is  explained  by 
the  fact,  that  the  transparency  which  balsam  gives,  inter- 
feres with  one  property  of  the  object,  and  yet  develops 
another  which  would  have  remained  invisible  if  preserved 
dry.  The  only  method  of  overcoming  this  difficulty  is  to 
keep  the  object  mounted  in  both  ways,  which  is  comparatively 
little  trouble. 

I  may  here  mention  that  many  prefer  the  lieberkuhn 
for  the  illumination  of  opaque  objects;  and  a  good  back- 
ground is  gained  by  putting  upon  the  under-side  of  the 
slide,  immediately  beneath  the  object,  a  spot  of  black  varnish, 
which  does  not  interfere  materially  with  the  light. 


90  PREPARATION   AND   MOUNTING 


CHAPTEE    IV. 

MOUNTING    IN     CANADA    BALSAM. 

THE  nature  and  use  of  this  substance  has  been  before  spoken 
of,  so  that  the  method  of  working  with  it  may  be  at  once 
described. 

Perfect  dryness  of  the  objects  is,  if  possible,  more  neces- 
sary in  this  mode  of  mounting  than  any  other,  as  dampness 
remaining  in  the  object  will  assuredly  cause  a  cloudiness  to 
make  its  appearance  in  a  short  time  after  it  is  fixed.  Where 
pressure  does  not  injure  the  specimens,  they  are  most  suc- 
cessfully treated  when  first  dried  betwixt  the  leaves  of  a 
book,  or  in  any  other  way  which  may  prove  most  convenient, 
as  noticed  in  Chapter  III. 

Before  describing  the  methods  of  proceeding  with  par- 
ticular objects,  general  rules  may  be  given  which  should  be 
observed  in  order  to  succeed  in  this  branch  of  mounting. 

As  the  object  is  to  be  thoroughly  immersed  in  the  balsam, 
it  is  evident  that  when  it  has  once  been  covered,  so  it  must 
remain,  unless  we  again  free  it  by  a  process  hereafter  men- 
tioned, which  is  very  troublesome ;  and  on  this  account  there 
must  be  nothing  whatever  in  the  balsam  except  the  object. 
The  inexperienced  may  think  this  an  unnecessary  caution ; 
but  the  greatest  difficulty  he  will  meet  with  is  to  get  rid  of 
minute  bubbles  of  air,  perhaps  invisible  to  the  naked  eye, 
which  appear  like  small  globules  when  under  the  microscope, 
and  render  the  slide  unsightly,  or  even  worthless.  Balsam 
dissolved  in  benzole  will  be  found  invaluable  in  mounting 
without  air -bubbles  j  if  a  few  are  left  in  the  specimen,  by 
the  next  morning  they  will  have  entirely  disappeared.  la 
making  this  solution  the  balsam  should  be  first  boiled 
gently  till  on  dropping  a  small  quantity  into  water  it  is 


OF  MICKOSCOPIC   OBJECTS.  91 

found  to  be  as  hard  as  resin,  the  softened  and  warm  solution 
may  be  now  poured  into  a  bottle,  and  when  cool  the  benzole 
added  in  sufficient  quantity  to  make  it  of  a  desirable  thick- 
ness. Ten  objects  out  of  eleven  contain  air,  or  at  least  aie 
full  of  minute  holes  which  are  necessarily  filled  with  it ;  so 
that  if  they  should  be  immersed  in  any  liquid  of  thick 
consistency,  these  cells  of  air  would  be  imprisoned,  ard 
become  bubbles.  The  air,  then,  must  be  removed,  and  this 
is  usually  accomplished  by  soaking  for  some  time  in  turpen- 
tine, the  period  required  differing  according  to  the  nature  of 
the  object.  In  some  cases,  the  turpentine  acts  upon  the 
colour,  or  even  removes  it  altogether,  so  that  it  must  be 
watched  carefully.  Often,  however,  this  is  an  advantage, 
as  where  the  structure  alone  is  wanted,  the  removal  of  the 
colouring  matter  renders  it  more  transparent.  There  are 
objects,  however,  which  retain  the  air  with  such  tenacity 
that  soaking  alone  will  not  remove  it.  If  these  will  bear 
•heat  without  being  injured,  they  may  be  boiled  in  turpentine, 
or  even  in  balsam,  when  the  air  will  be  partly  or  totally 
expelled.  But  where  heat  is  objectionable,  they  must  be 
immersed  in  the  turpentine,  and  so  submitted  to  the  action 
of  the  air-pump.  Even  with  this  aid,  sometimes  days  are 
required  to  accomplish  it  perfectly,  during  which  time  the 
air  should  be  exhausted  at  intervals  of  five  or  six  hours,  if 
convenient,  and  the  objects  turned  over  now  and  then. 

Many  complaints  are  made  concerning  turpentine,  both 
as  to  its  cleanliness  and  penetrating  power.  Most  of  these 
spring  from  the  fact  that  few  substances  in  the  market  vary 
so  much  as  turpentine  in  purity ;  all  sorts  of  rubbish  are 
sold  under  this  name,  and  now  benzole  is  employed  by  many 
in  all  cases  where  turpentine  alone  was  once  used. 

Sometimes  the  objects  are  so  minute  that  it  is  impossible 
to  submit  them  to  any  soaking,  and  in  this  case  they  must 
be  laid  upon  the  slide  at  once,  and  the  turpentine  applied 
to  them  there.  But  it  must  not  be  forgotten  that  there  are 
some  few  which  are  much  better  mounted  in  such  a  way 
that  the  balsam  may  thoroughly  surround,  and  yet  not 


92  PREPARATION   AND   MOUNTING 

penetrate,  the  substance  more  than  necessary.  Sections  of 
teeth  are  amongst  these,  but  they  will  be  noticed  in  another 
place,  and  some  insects  (see  Dr.  Carpenter)  when  required 
to  show  the  ramifications  of  the  tracheae. 

Having  freed  the  object,  then,  from  these  two  enemies — 
dampness  and  air — we  now  proceed  to  mount  it. 

The  slide  must  first  be  cleaned ;  then  on  the  centre  a 
quantity  of  balsam  must  be  placed  with  a  bluntly-pointed 
glass  rod,  according  to  the  size  of  the  object  about  to  be 
mounted.  To  this  a  slight  heat  must  be  applied,  which 
will  cause  any  bubbles  to  rise  from  the  surface  of  the  slide, 
so  that  they  may  be  readily  removed  with  a  needle.  The 
object  having  been  freed  from  all  air  by  steeping  in  turpen- 
tine, as  before  described,  and  then  from  superfluous  liquid 
by  a  short  drainage,  or  touch  upon  blotting-paper,  is  to  be 
carefully  laid  upon,  or  where  it  is  practicable  thrust  into, 
the  balsam  just  prepared  on  the  slide.  In  the  former 
case,  or  where  the  balsam  has  not  totally  covered  the  object,- 
a  small  quantity  must  be  taken,  warmed,  and  dropped  upon 
it,  and  any  bubbles  removed  by  the  needle  as  before.  To 
cover  this,  the  thin  glass  must  be  warmed,  and  beginning 
at  one  side,  allowed  to  fall  upon  the  balsam,  driving  a 
small  "  wave "  before  it,  and  thus  expelling  any  bubbles 
which  may  remain.  This  is  quite  as  safely  performed  (if 
not  more  so)  by  making  a  solution  of  balsam  in  turpentine 
of  the  consistency  of  thick  varnish  or  by  the  use  of  chloroform 
and  balsam,  as  mentioned  in  Chapter  II.  The  thin  glass  cover 
may  be  slightly  coated  with  this,  and  will  then  be  much 
less  liable  to  imprison  any  air,  which  frequently  happens 
when  the  cover  is  dry.  Bubbles,  however,  will  sometimes 
make  their  appearance  in  spite  of  all  care;  but  when  the 
object  is  comparatively  strong,  they  may  be  removed  by 
keeping  the  slide  rather  warm,  and  working  the  cover  a 
little,  so  as  to  press  them  to  one  side,  when  they  should  be 
immediately  removed  with  a  needle  point,  otherwise  they 
are  again  drawn  under. 

Where  the  slide  requires  keeping  warm  for  any  length  of 


OF   MICKOSCOHC   OBJECTS.  93 

time,  a  hot-water  bath  is  sometimes  made  use  of,  which  is 
simply  a  flat  tin,  or  other  metal  case,  with  a  mouth  at  the 
side,  that  when  the  hot  water  is  introduced  it  may  be  closed 
up,  and  so  retain  its  warmth  for  a  long  time.  An  excellent 
bath  may  be  made  of  an  ordinary  water-plate — costing 
about  Is.  9d.  This  may  be  filled  either  with  hot  water  or 
sand,  and  if  to  it  be  added  a  flat  tin  cover  such  as  is  used 
in  eating-houses,  costing  about  6d. — a  very  effective  oven 
for  baking  slides  is  the  result.  It  may  be  placed  on  the 
hob,  or  over  or  near  any  source  of  heat.  It  is  easy  to  add 
a  thermometer  if  necessary.  In  working,  the  slide  is  laid 
upon  it,  and  so  admits  of  longer  operations,  when  required, 
without  growing  cold.  Sometimes  a  spirit-lamp  is  placed 
under  it  to  keep  up  an  equal  heat  through  excessively  long 
processes.  Where  the  time  required,  however,  is  but  short, 
a  thick  brass  plate  is  sometimes  used  (see  Chapter  II.), 
which  may  be  heated  to  any  degree  that  is  required,  the  slide 
being  previously  placed  upon  it. 

Some  objects,  which  are  so  thin  that  they  are  usually 
floated  upon  the  slide,  as  before  stated,  require  no  steeping 
in  turpentine  or  other  liquid.  These  are  best  mounted  by 
covering  with  a  little  diluted  balsam,  and  after  this  has  had 
time  to  penetrate  the  substance,  ordinary  balsam  is  laid 
upon  it,  and  the  slide  finished  in  the  usual  manner. 

I  have  stated  that  balsam  is  usually  applied  to  the  slide 
and  objects  with  a  bluntly -pointed  glass  rod ;  but  for  the 
purpose  of  drawing  the  balsam  from  the  bottle,  and  convey- 
ing it  to  the  desired  place,  Dr.  Carpenter  uses  a  glass 
syringe  with  a  free  opening.  These  are  his  instructions  : — 
"  This  (the  syringe)  is  most  readily  filled  with  balsam,  in 
the  first  instance,  by  drawing  out  the  piston,  and  pouring 
in  balsam  previously  rendered  more  liquid  by  gentle  warmth; 
and  nothing  else  is  required  to  enable  the  operator  at  any 
time  to  expel  precisely  the  amount  of  balsam  he  may  require, 
than  to  warm  the  point  of  the  syringe,  if  the  balsam  should 
have  hardened  in  it,  and  to  apply  a  very  gentle  heat  to  the 
syringe  generally,  if  the  piston  should  not  then  be  readily 


94  PEEPARATION   AND   MOUNTING 

pressed  down.  When  a  number  of  balsam  objects  are  being 
mounted  at  one  time,  the  advantage  of  this  plan  in  regard 
to  facility  and  cleanliness  (no  superfluous  balsam  being 
deposited  on  the  slide)  will  make  itself  sensibly  felt,"  but 
the  collapsible  metal  capsules  are  certainly  the  best  and 
most  easily  managed. 

When  the  mounting  has  been  thus  far  accomplished, 
the  outer  wall  of  balsam  may  be  roughly  removed  after  a 
few  hours  have  elapsed;  but  great  care  is  necessary  lest 
the  cover  be  moved  or  disturbed  in  any  way.  In  this 
state  it  may  be  left  for  the  final  cleansing  until  the  balsam 
becomes  hard,  which  takes  place  sooner  or  later,  according 
to  the  degree  of  warmth  to  which  it  has  been  subjected. 
Many  advocate  baking  in  a  slow  oven  to  accelerate  this 
drying;  but  with  some  objects  even  this  heat  would  be 
too  great,  and  generally  a  mantel-piece,  or  other  place 
about  equal  to  it  in  temperature,  is  the  best  suited 
to  this  purpose ;  and  when  the  requisite  hardness  is 
attained,  the  slide  may  be  finished  as  follows: — With  a 
pointed  knife  the  balsam  must  be  scraped  away,  taking  care 
that  the  thin  glass  be  not  cracked  by  the  point  getting 
'under  it.  If  used  carefully,  the  knife  will  render  the  slide 
almost  clean;  but  any  minute  portions  which  still  adhere 
to  the  glass  must  be  rubbed  with  linen  dipped  in  turpentine 
or  spirit.  If  the  balsam  is  not  very  hard,  these  small 
fragments  are  readily  removed  by  folding  a  piece  of  paper 
tightly  in  a  triangular  form  with  many  folds,  and  damping 
the  point  with  which  the  glass  is  rubbed.  As  the  paper 
becomes  worn  with  the  friction,  the  balsam  will  be  carried 
off  with  it.  In  some  cases  I  have  found  this  simple  ex- 
pedient very  useful. 

Sometimes  the  object  to  be  mounted  is  of  such  a  thick- 
r.ess  as  to  require  a  cell.  For  this  purpose  glass  rings  are 
nsed  (as  described  in  Chapter  V.),  and  filled  with  balsam. 
The  best  mode  of  doing  this  is  thus  described  by  Mr.  T.  S. 
Kalph  in  the  Microscopic  Journal : — "  The  question  was 
asked  me  when  I  was  in  England,  if  I  knew  how  to  fill  a 


OF    MICROSCOPIC    OBJECTS.  95 

cell  with  Canada  balsam  and  leave  behind  no  air-bubbles  ? 
I  replied  in  the  negative ;  but  now  I  can  state  how  to 
accomplish  this.  Fill  the  cell  with  clear  spirit  of  turpentine, 
place  the  specimen  in  it,  have  ready  some  balsam  just  fluid 
enough  to  flow  out  of  the  bottle  when  warmed  by  the  hand ; 
pour  this  on  the  object  at  one  end,  and  gradually  inclining 
the  slide,  allow  the  spirit  of  turpentine  to  flow  out  on  the 
opposite  side  of  the  cell  till  it  is  full  of  balsam ;  then  take 
up  the  cover,  and  carefully  place  upon  it  a  small  streak  of 
Canada  balsam  from  one  end  to  the  other.  This,  if  laid  on 
the  cell  with  one  edge  first,  and  then  gradually  lowered 
until  it  lies  flat,  will  drive  all  the  air  before  it,  and  prevent 
any  bubbles  from  being  included  in  the  cell.  It  can  be 
easily  put  on  so  neatly  as  to  require  no  cleaning  when 
dry.  If  the  cover  be  pressed  down  too  rapidly,  the  balsam 
will  flow  over  it,  and  require  to  be  cleaned  off  when 
hardened,  for  it  cannot  be  done  safely  while  fluid  at  the 


Sometimes  with  every  care  bubbles  are  enclosed  in  the 
balsam,  injuring  objects  which  are  perhaps  rare  and  valuable. 
If  the  object  will  not  be  injured  by  heat,  carefully  warming 
the  slide  over  a  lamp  will  often  set  loose  and  remove  these 
pests ;  but  should  heat  be  objectionable,  or  the  bubbles  too 
closely  imprisoned,  the  whole  slide  must  be  immersed  in 
turpentine  until  the  cover  is  removed  by  the  solution  of  the 
balsam ;  and  the  object  must  be  cleansed  by  a  similar  steep- 
ing. It  may  then  be  remounted  as  if  new  in  the  manner 
before  described. 

The  balsam  and  chloroform  described  in  Chapter  II.  is 
thus  used ;  and  where  the  object  is  thin,  the  mounting  is 
very  easily  accomplished.  When  the  object  is  laid  upon  the 
slide  with  a  piece  of  glass  upon  it,  and  the  balsam  and 
chloroform  placed  at  the  edge  of  the  cover,  the  mixture  will 
gradually  flow  into  the  space  betwixt  the  glasses  until  the 
object  is  surrounded  by  it,'  and  the  unoccupied  portion  filled. 
The  chloroform  will  evaporate  so  quickly  that  the  outer  edge 
will  become  hard  in  a  very  short  time,  when  it  may  be 


96  PKEPA.RATION   AXD   MOUXTIXG 

cleaned  in  the  ordinary  way.  Sometimes  the  balsam  is 
dissolved  in  the  chloroform  without  being  first  hardened ; 
but  this  is  only  to  render  it  more  fluid,  and  so  give  the 
operator  less  chance  of  leaving  bubbles  in  the  finished  slide, 
as,  the  thicker  the  medium  is,  the  more  difficult  is  it  to  get 
rid  of  these  intruders. 

It  has  been  before  noticed  that  some  have  objected  to 
chloroform  and  balsam,  believing  that  it  became  clouded 
after  a  certain  time.  Perhaps  this  may  be  accounted  for 
in  part  by  the  fact  that  almost  all  objects  have  a  certain 
amount  of  dampness  in  them.  Others  are  kept  in  some 
preservative  liquid  until  the  time  of  mounting,  and  these 
liquids  generally  contain  certain  salts  (Chapter  V.).  If 
this  dampness,  as  well  as  all  traces  of  these  salts,  however 
small,  are  not  totally  removed — the  former  by  drying,  the 
latter  by  repeated  washings — the  addition  of  chloroform 
will  render  the  balsam  much  more  liable  to  cloudiness  than 
when  balsam  alone  was  used.  It  may  safely  be  affirmed  that 
benzole  will  be  found  in  all  cases  a  more  valuable  solvent  for 
Canada  balsam  than  chloroform. 

This  mode  of  employing  the  balsam,  however,  will  not  be 
always  applicable,  as  chloroform  acts  upon  some  substances 
on  which  balsam  alone  does  not.  Some  salts  are  even  soluble 
in  it,  the  crystals  appearing  after  a  few  days  or  weeks, 
whereas  in  balsam  alone  they  are  quite  permanent.  Ex- 
perience is  the  only  guide  in  some  cases,  whilst  in  others  a 
little  forethought  will  be  all  that  is  required. 

The  particular  methods  used  for  certain  objects  may  now 
be  entered  upon.  Many  of  the  Diatomaceae  and  fossil 
Infusoria,  as  they  are  sometimes  termed,  are  mounted  dry, 
and  cleaned  in  the  way  described  in  Chapter  III.  Others 
are  almost  always  placed  in  balsam,  except  where  they  are 
intended  to  be  used  with  the  lieberknhn  and  dark  back- 
ground, by  which  means'  some  of  them  are  beautifully  shown. 
The  usual  .way  of  mounting  them  in  balsam  is  as  follows : — 
Take  a  drop  of  the  water  containing  them,  place  it  upon 
the  slide,  and  evaporate  over  the  lamp,  whilst  with  a  needle 


OF   MICROSCOPIC   OBJECTS.  97 

they  may  be  dispersed  over  any  space  desired.  When  they 
are  thoroughly  dry,  drop  a  little  balsam  on  one  side,  and 
exclude  the  bubbles.  The  slide  may  then  be  warmed  to 
such  a  degree  that  the  balsam,  by  lifting  the  glass  at  one 
end,  will  be  carried  over  the  specimens,  which  may  then  be 
covered  with  thin  glass,  made  warm  as  before  described. 
Where  the  objects  are  quite  dry,  and  loose  upon  the  glass, 
it  requires  great  care  in  placing  the  cover  upon  them,  other- 
wise they  are  forced  to  one  edge,  or  altogether  from  tinder 
it,  in  the  wave  of  the  balsam.  For  this  reason,  Professor 
Williamson  adds  a  few  drops  of  gum-water  to  the  last 
washing,  which  causes  them  to  adhere  sufficiently  to  the 
glass  to  prevent  any  such  mishap. 

Mr.  T.  Gr.  Rylands's  method  differs  in  some  degree  from 
the  above,  and  is,  to  use  his  own  words,  as  follows : — Thick 
balsam  is  preferable,  and  the  burnt  covers  (see  Chapter  III.) 
to  be  mounted  are  laid  in  a  convenient  position,  with  the 
diatoms  upwards.  The  slides  required  having  been  care- 
fully cleaned  and  marked  on  the  under  side  with  a  ring  of 
ink  about  half  an  inch  in  diameter  by  the  aid  of  a  turntable 
to  point  out  the  centre,  a  drop  of  benzole  is  applied  by  a 
large  pin  to  the  diatoms  on  the  cover,  so  as  to  exclude  the 
air  from  the  valves  and  frustules.  The  slide  is  then  held 
over  the  lamp,  and  when  warm,  a  sufficiently  large  drop  of 
balsam  is  put  upon  it,  and  heated  until  it  begins  to  steam. 
If  small  bubbles  appear,  a  puff  of  breath  removes  them, 
The  slide  being  held  slightly  inclined  from  the  operator,  and 
the  drop  of  balsam  becoming  convex  at  its  lower  edge,  the 
cover  is  brought  in  contact  with  it  at  that  point,  gradually 
laid  down,  pressed  with  the  forceps,  and  brought  to  its 
central  position.  When  cool  the  superfluous  balsam  (if 
any)  is  removed  with  a  heated  knife-blade,  the  slide  cleaned 
with  a  little  turpentine,  and  finished  by  washing  in  a  hand- 
basin  with  soap  and  water.  In  this  process  there  is  no 
delay  if  the  balsam  be  sufficiently  thick,  as  the  slide  may  be 
cleaned  off  almost  before  it  is  cold. 

It  is  now  well  known  that  from  common  chalk  it  is  an 


98  PREPARATION   AND   MOUNTING 

easy  matter  to  obtain  interesting  specimens  of  Foraminifera. 
Scrape  a  small  quantity  of  chalk  from  the  mass  and  shake 
it  in  water ;  leave  this  a  few  minutes,  pour  the  water  away 
and  add  a  fresh  quantity,  shake  up  as  before,  and  repeat 
two  or  three  times.  Take  a  little  of  the  residue,  and  spread 
it  upon  the  slide,  and  when  quite  dry,  add  a  little  turpentine. 
When  viewed  with  a  power  of  two  hundred  and  fifty  dia- 
meters, this  will  generally  show  the  organisms  very  well. 
If  it  is  desired  to  preserve  the  slides,  they  may  then  be 
mounted  in  Canada  balsam.  Mr.  Guyon,  in  "  Becreative 
Science,"  observes  that  the  accumulation  of  the  powder,  by 
the  action  of  the  rain  or  exposure  to  the  atmospheric  action, 
at  the  foot  or  any  projection  of  the  chalk  cliffs,  will  afford 
us  better  specimens  than  that  which,  is  scraped,  as  the 
organisms  are  less  broken  in  the  former. 

Take  a  piece  of  chalk,  and  with  a  soft  tooth  or  nail  brush, 
brush  it  under  water,  and  then  wash  the  sediment  well  till 
the  water  is  not  coloured,  when  the  residue  will  be  nearly 
all  Foraminifera. 

The  above  is  the  most  simple  method  of  obtaining  Fora- 
minifera from  chalk,  but  is  not  so  satisfactory  when  any 
number  of  perfect  slides  is  wanted  for  the  cabinet.  I  shall, 
therefore,  give  additional  particulars  from  the  experience  of 
good  men.  But  some  specimens  of  chalk  seem  to  have 
undergone  such  powerful  action  that  no  perfect  forms  are 
found  in  them.  This  accounts  for  that  disappointment 
which  I  have  now  and  then  heard  expressed.  One  student 
says, — Take  about  one  ounce  of  chalk,  place  it  in  a 
quart  bottle  with  about  a  pint  of  water,  shake  it,  and  after 
a  few  moments  pour  off  the  milky  Huid  to  about  one  fourth. 
Add  more  fresh  water,  shake  and  pour  off,  waiting  longer 
each  time  for  it  to  settle.  Continue  ten  or  twelve  times  in 
one  day,  and  repeat  two  or  three  times  a  day  for  a  few  days, 
and  the  result  will  be  a  sediment  entirely  composed  of 
Foraminifera.  If  fragments  of  chalk  remain,  the  bottle  has 
not  been  sufficiently  shaken. 

Mr.  Bobertson  us(>s  a  somewhat  different  method.     Break 


OF    MICROSCOPIC    OBJECTS.  99 

a  lump  of  fresh  chalk  into  pieces  not  larger  than  a  walnut ; 
then]  crush,  but  not  grind,  lest  you  destroy  the  forms,  into 
a  coarse  powder  that  will  pass  a  somewhat  wide  sieve.  Tie 
this,  as  a  pudding,  in  a  stout  piece  of  calico.  Drop  into 
water  and  allow  the  bundle  to  become  saturated,  and  then 
knead  with  the  hands.  This  will  expel  a  quantity  of  milky 
water.  From  time  to  time,  after  allowing  the  fluid  to  drain 
off,  the  cloth  should  be  untied,  and  retied  more  closely  to 
the  mass ;  and  when  the  contents  are  reduced  to  about  one- 
third  of  their  original  bulk,  all  large  pieces  of  chalk,  portions 
of  spines  of  echini,  &c.,  should  be  removed,  lest  they  injure 
the  more  delicate  forms.  Care  must  be  taken  in  the 
kneading  when  the  greater  portion  of  the  chalk  has 
escaped,  and  at  last  the  bag  only  shaken  until  the  water 
flows  from  it  almost  clear.  The  wtole  may  then  be  trans- 
ferred to  a  bottle  of  clear  water  and  treated  as  before 
described.  The  results,  Mr.  Robertson  says,  will  be  satis- 
factory, and  the  chalk  must  be  very  poor  in  fossils  if  2  Ib. 
would  not  satisfy  any  microscopic  observer. 

When  the  Foraminifera  are  of  a  larger  size,  though  trans- 
parent enough  to  be  mounted  in  balsam,  the  air  must  be 
first  expelled  from  the  interior,  otherwise  the  objects  will  be 
altogether  unsatisfactory.  To  accomplish  this  they  must 
be  immersed  in  turpentine  and  submitted  to  the  action  of 
the  air-pump.  So  difficult  is  it  to  get  rid  of  this  enemy, 
that  it  is  often  necessary  to  employ  three  or  four  exhaus- 
tions, leaving  them  for  some  time  under  each.  When  all 
air  has  given  place  to  the  turpentine,  they  must  be  mounted 
in  the  ordinary  way. 

Of  all  objects  which  are  commonly  met  with,  few  are  such 
general  favourites  as  the  POLYCYSTIN^E  ;  and  deservedly  so. 
Their  forms  are  most  beautiful,  and  often  peculiar — stars 
varying  in  design,  others  closely  resembling  crowns  ;  the 
Astromma  Aristotelis  like  a  cross,  and  many  whose  shapes 
no  words  could  describe.  The  greater  part,  perhaps,  of 
those  which  are  usually  sold,  are  from  the  rocky  parts  of 
Bermuda ;  but  they  are  also  found  in  Sicily,  some  parts  of 
H  2 


100  PREPARATION   AND   MOUNTING 

Africa  and  America.  They  are  usually  mounted  in  balsam, 
but  are  equally  beautiful  mounted  dry,  and  used  with  the 
lieberkuhn.  They  require  as  much  care  in  cleaning  as  the 
Diatomacese,  but  the  process  is  a  different  one.  Sometimes 
this  is  effected  by  simply  washing  until  they  are  freed  from 
all  extraneous  matter;  but  this  is  seldom  as  effectual  as  it 
should  be.  In  the  Microscopic  Journal  Mr.  Furlong  gives 
the  following  method  of  treatment  as  the  best  he  knows  : — 
Procure — 

A  large  glass  vessel  with  3  or  4  quarts  of  water. 

New  tin  saucepan  holding  1  pint. 

2  thin  precipitating  glasses  holding  10  oz.  each. 
Take  3  oz.  of  dry  Barbadoes  earth  (lumps  are  best),  and 
break  into  rather  small  fragments.  Put  3  or  4  oz.  of  com- 
mon washing  soda  into  the  tin  and  half  fill  it  with  water. 
Boil  strongly,  and  having  thrown  in  the  earth,  boil  it  for 
half  an  hour.  Pour  nine-tenths  of  this  into  the  large  glass 
vessel,  and  gently  crush  the  remaining  lumps  with  a  soft 
bristle  brush.  Add  soda  and  water  as  before,  and  boil  again  ; 
then  pour  off  the  liquid  into  the  large  vessel,  and  repeat 
until  nothing  of  value  remains.  Stir  the  large  vessel  with 
an  ivory  spatula,  let  it  stand  for  three  minutes,  and  pour 
gently  off  nine-tenths  of  the  contents,  when  the  shells  will  be 
left,  partially  freed  only,  like  sand. 

2ND  PROCESS. — Put  common  washing  soda  and  water  into 
the  tin  as  before,  and  having  placed  the  shells  therein,  boil 
for  an  hour.  Transfer  to  the  large  vessel  as  before,  and 
after  allowing  it  to  stand  for  one  minute,  pour  off.  Each 
washing  brings  off  a  kind  of  "flock,"  which  seems  to  be 
skins. 

SRD  PROCESS. — Put  the  shells  in  a  precipitating  glass  and 
drain  off  the  water  until  not  more  than  -|-  oz.  remains.  Add 
half  a  teaspoonful  of  bicarbonate  of  soda,  dissolve,  and  then 
pour  in  gently  1  oz.  of  strong  sulphuric  acid.  This  liberates 
the  "  flock,"  &c.,  and  leaves  the  shells  beautifully  trans- 
parent. Wash  well  now  with  water  to  get  rid  of  all  salts 
and  other  soluble  matter. 


OF   MICROSCOPIC    OBJECTS.  101 

Some  of  the  large  shells  are  destroyed  by  this  method, 
but  none  that  are  fit  for  microscopic  use.  An  oblique  light 
shows  these  objects  best. 

These  are  sometimes  treated  in  the  manner  described  in 
Chapter  III.,  where  the  diatoms  are  spoken  of,  but  many 
forms  are  liable  to  be  injured  by  this  severe  process. 

It  has  been  before  stated  that  some  of  the  zoophytes  may 
be  mounted  dry,  and  others  examined  as  opaque  or  trans- 
parent objects  according  to  their  substance.  They  are  very 
interesting  when  examined  in  the  trough  whilst  living,  but 
to  preserve  many  of  them  for  future  examination  they  must 
be  mounted  in  some  preservative  medium.  Sometimes  this 
may  be  one  of  the  liquids  mentioned  in  Chapter  "V.,  but 
if  possible  they  should  be  kept  in  balsam,  as  there  is  less 
danger  of  injury  by  accident  to  this  kind  of  slide.  This 
method  of  mounting  presents  some  difficulties,  but  I  think 
that  all  agree  as  to  the  trustworthiness  of  Dr.  Golding 
Bird's  information  on  the  subject,  which  appeared  in  the 
Microscopic  Journal.  Of  this,  space  forbids  rue  to  give  more 
than  a  condensed  account,  but  I  hope  to  omit  nothing  of 
moment  to  the  reader  for  whom  these  pages  are  written. 

After  stating  that  there  are  few  who  are  not  familiar 
with  these  exquisite  forms,  and  have  not  regretted  the  great 
loss  of  beauty  they  sustain  in  drying,  he  informs  us  that 
from  their  so  obstinately  retaining  air  in  the  cells  and  tubes 
when  dried,  it  is  hardly  practicable  to  get  rid  of  it ;  and  they 
also  shrivel  up  very  seriously  in  the  process  of  drying.  The 
following  plan,  however,  he  has  found  almost  faultless  in 
their  preparation. 

To  preserve  them  with  extended  tentacles,  they  should 
be  plunged  in  cold  fresh  water,  which  kills  them  so  quickly 
that  these  are  not  often  retracted.*  The  specimens  should 
be  preserved  in  spirit  until  there  is  leisure  to  prepare  them  ; 

*  It  has  been  stated  that  the  best  method  of  killing  zoophytes  is  to 
drop  alcohol,  French  brandy,  or  benzole  into  the  salt  water  in  which 
they  are  placed ;  as  this  will  cause  no  retraction  of  tentacles  if  it  bo 
done  gradually. 


102  PREPARATION   AND   MOUNTING 

if,  however,  they  have  been  dried,  they  should  be  soaked  in 
cold  water  for  a  day  or  two  before  being  submitted  to  the 
following  processes : — 

1.  After  selecting  perfect  specimens  of  suitable  size,  im- 
merse them  in  water  heated  to  about  120°,  and  place  them 
under  the  receiver  of  an  air-pump.     Slowly   exhaust  the 
air,  when  bubbles  will  rise  and  the  water  appear  to  be  in  a 
state  of  active  ebullition.     After  a  few  minutes  re-admit  the 
air  and  again  exhaust,  repeating  the   process  three  or  four 
times.     This  will  displace  the  air  from  most,  if  not  all,  of 
the  class. 

2.  Remove  the  specimens  and  allow  them  to  drain  upon 
blotting-paper  for  a  few  seconds ;  then  place  them  in  an 
earthen  vessel  fitted  with  a  cover,  and  previously  heated  to 
about  200°.     This  heat  may  be  easily  got  by  placing  the 
vessel  for  a  short  time  in  boiling  water,  wiping  it  imme- 
diately before  using,  with  a  thick  cloth.     The  specimens  are 
then   dropped  into  this,  covered  with   the  lid,  and  imme- 
diately placed    under    the  receiver   of   the   air-pump,   and 
the   air  rapidly  exhausted.     By  this  means  they  are  dried 
completely,  and  so  quickly  that  the  cells  have  no  time  to 
wrinkle. 

3.  In  an  hour  or  two  remove  them  from  the  air-pump 
and  drop  them  into  a  vessel  of  perfectly  transparent  cam- 
phine.     This   may  be  quite  cold  when  the  horny,  tubular 
polypidoms,  as  those  of  the  Sertularife,  are  used ;  but  should 
be  previously  heated  to  100°  when  the  calcareous,  cellular 
Polyzoa  are  the  objects  to  be  preserved.     The  vessel  should 
be  covered  with  a  watch-glass   and   placed   under  the  re- 
ceiver, the  air  being  exhausted  and  re-admitted  two  or  three 
times. 

4.  The  slide  which  is  to  receive  the  specimen   should  be 
well  cleaned  and  warmed  so  as  to  allow  the  balsam  to  flow 
freely  over  it.     This  must  be  applied  in  good  quantity,  and 
air-bubbles  removed  with  the  needle-point.     Take  the  poly- 
pidom  from  the  camphine,  drain  it  a  little,  and   with  the 
forceps  immerse  it  fully  in  the  balsam.     The  glass  to  be 


OF  MICROSCOPIC  OBJECTS.  103 

laid  upon  it  should  be  warmed  and  its  surface  covered  with 
a  thin  layer  of  balsam,  and  then  lowered  gradually  upon 
it,  when  no  bubbles  should  be  imprisoned.  A  narrow- 
piece  of  card-board  at  each  end  of  the  object,  for  the 
cover  to  rest  upon,  prevents  any  danger  of  crushing  the 
specimen. 

This  mode  of  mounting  polypidoms,  &c.,  seema  to  give 
almost  the  complete  beauty  of  the  fresh  specimens.  They 
are  very  beautiful  objects  when  viewed  with  common  light, 
but  much  more  so  when  the  polarizer  is  used  (iti  the  manner 
described  a  little  farther  on). 

To  the  above  instructions  there  can  be  little  to  add ;  bat 
I  may  here  mention  that  some  yonng  students  may  not  be 
possessed  of  the  air-pump,  and  on  this  account  put  aside  all 
search  for  those  specimens  which  need  little  looking  for  at 
the  seaside.  Many  of  these,  however,  though  they  lose  some 
beauty  by  the  ordinary  mode  of  drying,  will,  by  steeping  for 
some  time  in  turpentine,  not  only  be  freed  from  the  air- 
bubbles,  but  suffer  so  little  contraction  that  they  are  a 
worthy  addition  to  the  cabinet. 

Another  class  of  objects  is  the  spicula  met  with  in 
sponges,  &c.  These  are  often  glass-like  in  appearance  and 
of  various  shapes ;  many  are  found  resembling  needles 
(whence  their  name) ;  some  from  the  synapta  are  anchor- 
like.'whilst  others  are  star-like  and  of  complex  and  almost 
indescribable  combinations.  As  some  of  these  are  composed 
of  silex  and  are  consequently  not  injured  by  the  use  of  nitric 
acid,  the  animal  substance  may  be  removed  by  boiiing  them 
in  it.  Those,  however,  which  are  calcareous  must  be  treated 
with  a  strong  solution  of  potash  instead ;  but  whichever 
way  is  used,  of  course  they  must  afterwards  be  freed  from 
every  trace  of  residue  by  careful  washing. 

These  spicules  may  be  often  found  amongst  the  sand 
which  generally  accumulates  at  the  bottom  of  the  jars  in 
which  sponges  are  kept  by  those  who  deal  in  them,  and 
must  be  picked  out  with  a  camel-hair  pencil.  The  speci- 
mens obtained  by  this  means  will  seldom  if  ever  require 


104  PREPARATION   AND   MOUNTING 

any  cleaning  process,  as  they  are  qnite  free  from  animal 
matter. 

In  the  former  chapter  were  noticed  those  insects  or  parts 
of  them  which  are  usually  mounted  dry.  When  they  are 
large  and  too  opaque  to  admit  of  the  dry  treatment,  they 
must  be  preserved  in  Canada  balsam  or  fluid.  The  first  of 
these  may  now  be  considered. 

It  may  be  here  mentioned,  that  with  these  objects  much 
heat  must  not  be  employed,  as  it  would  in  some  instances 
give  rise  to  a  cloudiness,  and  almost  invariably  injure  them. 

In  killing  the  insect  it  is  necessary  not  to  rub  or  break 
any  part  of  it.  This  may  be  performed  by  placing  it  in  a 
small  box  half  filled  with  fragments  of  fresh  laurel-leaves, 
by  immersion  in  turpentine  or  strong  spirit,  as  also  in  solu- 
tions of  various  poisonous  salts.  After  which  it  may  be 
preserved  for  some  time  in  turpentine  or  other  preservative 
liquid  (Chapter  V.)  until  required.  As  an  assistance  to  the 
student,  I  believe  that  I  can  do  no  better  than  give  him  the 
plan  pursued  by  my  friend  Mr.  Hepworth,  whose  specimens 
are  in  every  way  satisfactory;  but  when  his  method  is  used, 
the  insects  must  not  have  been  placed  in  turpentine  for 
preservation  : — 

"After  destroying  the  insects  in  chloroform  or  sulphuric 
ether  (methylated  being  cheaper),  wash  them  thoroughly  in 
a  wide-necked  bottle,  half-filled,  with  two  or  three  waters; 
the  delicate  ones  requiring  great  care.  Then  immerse  them 
in  liquid  potash  (or  Brandish's  solution,  which  is  stronger 
than  the  usual  preparation),  and  let  them  remain  a  longer 
or  shorter  time  according  to  their  texture.  When  ready  to 
remove,  put  one  by  one  into  a  small  saucer  of  clear  water, 
and  with  a  camel-hair  pencil  in  each  hand  press  them  flat 
to  the  bottom,  holding  the  head  and  thorax  with  the  left- 
hand  brush,  and  applying  pressure  with  the  other  from  above, 
downwards,  giving  the  brush  a  rolling  motion,  which  gene- 
rally expels  the  contents  of  the  abdomen  from  the  thorax. 
A  minute  roller  of  pith  or  cork  might  be  used  instead  of  the 
brash.  In  larger  objects,  use  the  end  of  the  finger  to  flatten 


OF   MICROSCOPIC    OBJECTS.  105 

them.  Large  objects  require  more  frequent  washing,  as  it  ia 
desirable  to  remove  the  potash  thoroughly,  or  crystals  are 
apt  to  form  after  mounting.  Having  placed  them  on  the 
slides  with  thin  glass  covers,  tied  down  with  thread,*  dry 
and  immerse  them  in  rectified  spirits  of  turpentine ;  place 
the  vessel  under  the  receiver  of  an  air-pump,  and  keep  it 
exhausted  until  the  turpentine  has  taken  the  place  of  the 
air-bubbles  ;  they  are  then  ready  for  the  application  of  the 
balsam.  Larger  objects  may  often  with  advantage  be  trans- 
ferred to  a  clean  slide,  as  during  the  drying  there  is  con- 
siderable contraction,  and  an  outline  showing  this  often 
remains  beyond  the  margin.  When  closely  corked,  they  may 
remain  in  the  spirits  two  or  three  months.  As  you  take 
them  from  the  bottle,  wipe  as  much  turpentine  off  as  possi- 
ble before  removing  the  thread,  and  when  untied  carefully 
wipe  again,  placing  the  finger  on  one  end  of  the  cover  whilst 
you  wipe  the  other,  and  vice  versa.  By  this  means  you 
remove  as  much  turpentine  from  under  the  cover  as  is 
necessary ;  then  drop  the  balsam,  thinned  with  chloroform 
(see  Chapter  II.},  upon  the  slide,  letting  the  fluid  touch  the 
cover,  when  it  will  be  taken  in  between  the  surfaces  by 
capillary  attraction  ;  and  after  pressing  the  cover  down,  it 
may  be  left  to  dry,  or  yon  may  hold  the  slide  over  a  spirit- 
lamp  for  a  few  seconds  before  pressing  down  the  cover.  If 
heat  is  not  applied,  they  are  much  longer  in  drying,  but  are 
more  transparent.  If  made  too  hot,  the  boiling  disarranges 
the  objects,  and  if  carried  too  far,  will  leave  only  the  resin  of 
the  balsam,  rendering  it  so  brittle  that  the  cover  is  apt  to 
fly  off  by  a  fall  or  any  jar  producing  sufficient  concussion. 
Never  lift  the  cover  up,  if  possible,  during  the  operation,  as 
there  is  danger  of  admitting  air.  A  few  bubbles  may  appear 
immediately  after  mounting,  but  they  generally  subside  after  a 
few  hours,  being  only  the  chloroform  or  turpentine  in  a  state 
of  vapour,  which  becomes  condensed." 

*  This  applies  to  the  more  delicate,  which  will  not  bear  transfer- 
ring after  being  once  spread  out  and  dried. 


106  PREPARATION   AND   MOUNTING 

This  method  of  preparing  and  mounting  insects  I  can 
strongly  recommend  as  giving  first-rate  results;  but  where 
the  specimens  are  small,  they  seldom  need  the  soaking  in 
caustic  potash  which  larger  ones  must  have.  It  is  only 
necessary  to  leave  them  awhile  in  turpentine,  especially 
when  they  have  been  first  dried  with  gentle  pressure  between 
two  glasses,  and  then  mount  with  balsam  in  the  ordinary 
way.  With  many,  even  of  the  larger  insects,  by  soaking 
them  in  turpentine  or  oil  of  cloves  for  a  longer  time,  they 
are  made  so  mnch  more  transparent  and  even  colourless, 
as  to  exhibit  their  internal  organs  (which  are  visible  in 
layers,  by  the  aid  of  the  binocular  microscope),  the  muscles 
of  the  legs,  &c.  They  become  also  very  beautiful  objects  for 
the  polariscope. 

Amongst  the  insect  tribes  there  is  abundant  employment, 
especially  for  the  lower  powers  of  the  microscope.  But  if 
the  deeper  wonders  and  beauties  of  the  animal  economy 
are  to  be  sought  out  and  studied,  it  is  desirable  that  the 
various  parts  should  be  set  separately,  in  order  that  they 
may  receive  a  more  undivided  attention,  as  well  as  be  ren- 
dered capable  of  being  dealt  with  under  the  higher  powers. 
We  will  therefore  briefly  consider  the  treatment  which  the 
different  portions  require. 

The  eyes  of  butterflies,  and  indeed  of  almost  all  insects, 
afford  materials  for  a  study  which  is  complete  in  itself. 
When  examined  with  a  tolerably  high  power,  instead  of 
finding  each  eye  with  an  unbroken  spherical  surface,  it  is 
seen  that  many  are  composed  of  thousands  of  hexagonal 
divisions,  each  being  the  outer  surface  of  a  separate  portion 
termed  the  ocellus.  In  others  these  divisions  are  square ; 
but  in  all  there  is  a  layer  of  dark  pigment  surrounding  their 
lower  parts.  The  ocelli  may  be  partly  removed  from  the 
eye,  which  will  show  how  their  tapering  forms  are  arranged. 
But  here  we  have  to  consider  how  to  place  them  in  balsam 
for  preservation.  The  eye  being  removed  from  the  insect, 
and  the  dark  pigment  removed  by  the  use  of  a  camel-hair 
pencil,  must  be  allowed  to  remain  in  turpentine  at  least  for 


OF   MICROSCOPIC   OBJECTS.  107 

some  days.  The  turpentine  should  then  be  renewed  and 
the  eye  well  washed  in  it  just  before  it  is  to  be  mounted. 
It  may  then  be  set  in  balsam  in  the  same  way  as  any  other 
object ; — but  here  a  difficulty  is  met  with.  The  eye  being 
spherical  upon  the  surface  required,  must  necessarily  be 
"  folded  "  or  broken  in  attempting  to  flatten  it.  This  diffi- 
culty may  be  often  overcome  by  cutting  a  number  of  slits 
round  the  edges ;  but  some  object  to  this  mode  of  treatment, 
and,  where  it  is  practicable,  it  is  much  more  satisfactory  to 
mount  one  in  the  natural  rounded  form  and  another  flat. 
Instead,  however,  of  mounting  the  organ  whole,  four  or  five 
slides  may  be  procured  from  each  of  the  larger  ones,  such  as 
those  of  the  dragon-fly,  &c. 

The  antennae  also  are  often  mounted  on  separate  slides, 
as  being  better  suited  for  higher  powers  and  more  minute 
examination  than  when  connected  with  the  insect.  These 
two  projecting  organs,  issuing  from  the  head,  are  jointed, 
and  moveable  at  will.  They  differ  very  much  in  form 
amongst  the  various  species,  and  are  well  worth  the  atten- 
tion of  the  microscopist.  They  are  usually  mounted  with 
the  head  attached,  and  perhaps  they  are  more  interesting 
when  thus  seen.  Some  few  are  very  opaque ;  to  prepare 
these  the  following  method  has  been  advised,  though  it  is 
far  better  to  view  them  as  opaque  objects : — 

Bleach  the  antennae  by  soaking  in  the  following  solution 
for  a  day  or  two  : — 

Hydrochloric  acid,  10  drops. 
Chlorate  of  potash,  \  drachm. 
Water,  1  oz. 

This  will  render  them  transparent.  Wash  well,  dry,  and 
mount  in  Canada  balsam.  Instead  of  the  above,  a  weak 
solution  of  chloride  of  lime  may  be  used,  by  which  means 
the  nerves  will  be  well  shown.  Many,  however,  are  rendered 
transparent  enough  by  simply  soaking  in  turpentine  for  a 
longer  or  shorter  time.  Where  the  antennas,  however,  are 
"Plumose,"  or  feather-like,  extreme  care  is  required  in 


108  PREPARATION   AND   MOUNTING 

mounting,  though  the  difficulty  is  not  so  great  as  some  seem 
to  think.  If  they  are  first  dried  with  gentle  pressure,  and 
then  subjected  to  the  action  of  the  air-pump  in  a  small 
quantity  of  turpentine  until  the  air  is  thoroughly  expelled, 
they  can  be  easily  finished  upon  the  slide,  especially  when 
balsam  and  chloroform  are  used. 

Insects  supply  us  with  another  series  of  beautiful  objects, 
viz.,  the  feet*  These  are  sometimes  simply  dried  and 
mounted  without  any  medium,  as  before  mentioned ;  but 
most  of  them  are  rendered  much  more  fit  for  examination 
by  using  balsam  in  their  preservation,  as  it  greatly  increases 
their  transparency.  The  smaller  kinds  may  be  dried  with 
gentle  pressure  betwixt  blotting-paper,  and  then  immersed 
for  some  days  in  turpentine,  without  requiring  the  treat- 
ment with  liquor  potassae.  This  immersion  will  render  them 
beautifully  transparent,  when  they  may  be  mounted  in 
balsam,  in  the  usual  manner. 

It  is,  however,  sometimes  found  difficult  to  fix  the  feet 
when  expanded,  in  which  state  the  interest  of  the  object  is 
greatly  increased.  Mr.  Ralph  recommends  the  following 
mode : — "  First  wash  the  feet,  while  the  insect  is  yet  alive, 
with  spirits  of  wine ;  then,  holding  it  by  a  pair  of  forceps 
close  to  the  edge  of  a  clean  piece  of  glass,  the  insect  will 
lay  hold  of  the  upper  surface  by  its  foot ;  suddenly  drop 
another  small  piece  of  glass  over  it,  so  as  to  retain  the  foot 
expanded,  and  cut  it  off  with  a  pair  of  scissors,  tie  up 
and  soak  to  get  rid  of  air."  Mr.  Hepworth  says  that  he 
never  found  any  difficulty  in  expanding  the  foot  on  a 
drop  of  water  or  well-wetted  slide,  and  laying  a  thin  glass 
cover  over  it,  tying  with  thread,  drying,  and  immersing  in 
turpentine. 

The  moutb,  also,  with  its  organs,  is  an  interesting  object 
in  many  insects.  That  of  the  common  fly  is  often  used, 
and  is  comparatively  easy  to  prepare.  By  pressing  the 
head,  the  tongue  (as  it  is  commonly  termed)  will  be  forced 

*  See  Mr.  Hepworth's  interesting  articles  on  the  fly's  foot  in  the 
second  and  third  volumes  of  the  Microscopic  Journal. 


OF   MICROSCOPIC   OBJECTS.  109 

to  protrude,  when  it  must  be  secured  by  the  same  means  as 
the  foot,  and  may  be  subjected  to  the  soaking  in  turpentine, 
and  mounted  as  usual.  The  honey-bee  is,  however,  very 
different  in  formation,  and  is  well  worth  another  slide ; 
indeed,  even  in  insects  of  the  same  class,  the  differences  are 
many  and  interesting.  There  is  another  good  friend  to 
the  Microscopic  Cabinet,  the  large  water-beetle,  "  Dyticus 
marginalia" ;  and  he  is  by  no  means  uncommon,  as  he  may 
be  met  with  in  many  old  ponds.  If  his  wings  are  taken, 
dried,  and  mounted  in  balsam,  beautiful  circles  with  crosses 
make  their  appearance  when  examined  by  the  aid  of 
polarized  light.  But  what  are  commonly  termed  his 
suckers  are  perhaps,  his  most  popular  gifts.  On  his  an- 
terior legs  will  be  found  small  discs  attached  to  central 
members  (making  the  whole  an  exact  resemblance  of  a  boy's 
sucker),  which  may  be  readily  cut  off,  placed  on  the  slide, 
and  mounted  in  balsam.  The  Dyticus  also  gives  splendid 
examples  of  spiracles ;  but  this  will  be  mentioned  where 
dissection  is  treated  of. 

Another  worthy  object  of  study  is  the  respiration  of 
insects,  which  is  effected  by  tracheae  or  hollow  tubes,  which 
generally  run  through  the  body  in  one  or  more  large  trunks, 
branching  out  on  every  side.  These  terminate  at  the  sur- 
face in  openings,  which  are  termed  spiracles,  or  breathing 
organs.  The  tracheae  often  present  the  appearance  of  tubes, 
constructed  of  a  spiral  thread,  somewhat  resembling  the 
spiral  fibres  of  some  plants.  These  are  very  beautiful 
objects,  and  are  generally  mounted  in  balsam,  for  which 
reason  they  are  mentioned  here ;  but  as  they  evidently 
belong  to  the  dissecting  portion,  they  will  be  fully  treated  of 
in  another  place. 

Amongst  the  parasitic  insects  a  great  variety  of  micro- 
scopic subjects  will  be  found.  As  these  are  usually  small, 
they  may  be  killed  by  immersion  in  spirits  of  turpentine; 
and,  if  at  all  opaque,  may  be  allowed  to  remain  in  the 
liquid  until  transparent  enough,  and  then  mounted  in 
Canada  balsam. 


110  PREPARATION  AND  MOUNTING 

The  acarida,  or  mites  and  ticks,  are  well  known ;  none, 
perhaps,  better  than  those  which  are  so  often  found  upon 
cheese.  Flour,  sugar,  figs,  and  other  eatables  are  much 
infested  by  them;  whilst  the  diseases  called  the  itch  in  man, 
and  the  mange  in  animals,  are  produced  by  creatures 
belonging  to  this  tribe.  These  insects  are  sometimes  mounted 
by  simply  steeping  them  in  turpentine,  and  proceeding  as 
with  other  insects.  The  Micrographic  Dictionary  gives 
the  following  directions  as  to  mounting  parts  of  these: — 
"  The  parts  of  the  mouth  and  the  legs,  upon  which  the 
characters  are  usually  founded,  may  be  best  made  out  by 
crushing  the  animals  upon  a  slide  with  a  thin  glass  cover, 
and  washing  away  the  exuding  substance  with  water  :  some- 
times hot  solution  of  potash  is  requisite,  with  the  subsequent 
addition  of  acetic  acid,  and  further  washing.  When  after- 
wards dried  and  immersed  in  Canada  balsam,  the  various 
parts  become  beautifully  distinct,  and  may  be  permanently 
preserved." 

Feathers  of  different  kinds  of  birds  are  usually  mounted 
in  balsam  when  required  to  show  much  of  the  structure. 
This  is  particularly  interesting  when  the  feathers  are  small, 
as  they  then  show  the  inner  substance,  or  pith,  as  it  may  be 
termed,  with  the  cells,  &c.  The  "  pinnae,"  or  soft  branches 
of  the  feathers,  will  be  found  of  various  constructions  ;  some 
possessing  hooks  along  one  side,  whereby  they  fasten  them- 
selves to  their  neighbours ;  others  branching  out,  with 
straight  points  somewhat  resembling  the  hairs  from  certain 
caterpillars.  But,  of  course,  when  the  metallic-looking 
gorgeous  colours  are  all  that  is  required  to  be  shown,  and 
reflected  light  used  (as  with  the  feathers  of  the  humming- 
bird, peacock,  &c.),  it  is  much  better  that  they  should  be 
mounted  dry,  as  in  Chapter  III. 

The  seeds  and  pollen  of  plants  are  most  frequently 
mounted  dry,  as  mentioned  in  Chapter  III. ;  but  thu  more 
transparent  of  the  former,  and  the  darker  kinds  of  the  latter, 
are  perhaps  better  seen  in  Canada  balsam.  There  is 
nothing  particular  to  be  observed  in  the  manipulation,  except 


OF   MICROSCOPIC   OBJECTS.  Ill 

that  the  glass  cover  must  be  applied  lightly,  otherwise  the 
grains  may  be  crushed.  There  are  some  objects  which 
cannot  be  shown  in  a  perfect  manner  when  mounted  dry, 
but  when  immersed  in  balsam  become  so  very  transparent 
that  they  are  almost  useless.  To  avoid  this,  it  has  been  re- 
commended to  stain  the  objects  any  colour  that  may  be  con- 
venient, and  afterwards  mount  in  balsam  in  the  ordinary 
manner. 

Permanent  dyes,  however,  for  these  minute  objects  are 
not  so  readily  procurable.  My  friend  Mr.  Abbey  showed 
me  that  what  was  permanent  with  vegetable  matter  of  one 
kind  was  totally  untrustworthy  with  another.  The  most 
useful  that  I  have  tried  is  Magenta,  and  the  colour  is  a 
convenient  one.  Whatever  is  used  for  this  purpose  should 
be  in  solution,  and  the  object  steeped  for  awhile  and  after- 
wards thoroughly  washed,  in  order  that  no  superfluous  salt 
may  remain.  Tnere  are  many  liquids  now  sold  by  every 
chemist  which  will  help  the  student  in  this  respect. 

Most  objects  intended  for  the  polariscope  may  be  mounted 
in  Canada  balsam  ;  but  there  are  some  exceptions  to  this. 
Many  of  the  salts  are  soluble  in  this  medium,  or  their  forms 
so  injured  by  it,  that  gljcerine  or  oil  has  to  be  used  (see 
Chapter  V.) :  others  must  be  left  in  the  dry  form,  as  before 
mentioned;  and  pome  few  it  is  impossible  to  preserve  un- 
changed for  any  length  of  time.  Crystals,  however,  are 
amongst  the  most  beautiful  and  interesting  subjects  for 
polarization;  and  it  is  very  probable  that,  by  the  aid  of  the 
polariscopp,  new  and  valuable  facts  are  yet  to  be  made 
known.  For  one  who  finds  pleasure  in  form  and  colour, 
there  is  a  field  here  which  will  only  open  wider  upon  him  as 
he  advances  ;  and  instead  of  being  in  anywise  a  merely 
mechanical  occupation,  it  requires  deep  and  careful  study. 
The  little  here  said  on  the  subject  will  show  this  in  some 
degree. 

With  almost  every  salt  the  method  of  crystallization  must 
be  modified  to  obtain  the  best  forms  ;  I  may  even  go  further 
than  this,  and  say  that  it  is  possible  to  change  these  forms 


112  PREPARATION   AND   MOUNTING 

to  such  a  degree  that  the  eye  can  perceive  no  relationship 
to  exist  between  them.  If  a  solution  of  sulphate  of  iron  be 
made,  a  small  quantity  spread  evenly  upon  a  slide,  and  then 
suffered  to  dry  whilst  in  a  flat  position,  the  crystals  often 
resemble  the  fronds  of  the  common  fern  in  shape.  But  if, 
whilst  the  liquid  is  evaporating,  it  is  kept  in  motion  by 
stirring  with  a  thin  glass  rod,  the  crystals  form  separately, 
each  rhombic  prism  having  its  angles  well  defined,  and 
giving  beautiful  colours  with  the  polarized  light.  Again, 
pyro-gallic  acid,  when  allowed  to  flow  evenly  over  the  slide 
in  a  saturated  solution,  covers  the  surface  in  long  needles, 
which  are  richly  coloured  by  polarized  light ;  but  if  any 
small  portion  of  dust  or  other  matter  should  form  a  nucleus 
around  which  these  needles  may  gather,  the  beauty  is 
wonderfully  increased.  A  form  very  closely  resembling  the 
"  eye  "  of  the  peacock's  tail,  both  in  form  and  colour,  is  then 
produced,  which  to  one  uninitiated  in  crystallography  bears 
very  little  resemblance  to  the  original  crystal.  From  these 
simple  facts  it  will  be  clearly  seen  that  in  this,  as  in  every 
other  department,  study  and  experience  are  needful  to  give 
the  best  results. 

By  dropping  a  saturated  solution  of  any  salt  into  alcohol 
— where  it  is  not  soluble  in  the  alcohol — crystals  are  in- 
stantaneously produced,  and  the  results  are  often  very  curious 
and  beautiful.  These  crystals  can  easily  be  taken  up  by  a 
pipette — deposited  upon  a  slide,  and,  after  having  been 
allowed  to  dry  spontaneously — mounted  in  balsam. 

To  obtain  anything  like  uniformity  in  the  formation  of 
crystals  upon  the  glass  slide,  every  trace  of  grease  must  be 
removed  by  cleaning  with  liquor  potassae  or  ammonias  im- 
mediately before  using,  care  also  being  taken  that  none  of 
the  agent  is  left  upon  the  slide,  otherwise  it  may  in- 
terrupt and  change  their  relative  position,  and  even  their 
form. 

Amongst  those  which  are  generally  esteemed  the  most 
beautiful,  are  the  crystals  of  oxalurate  of  ammonia.  The 
preparation  of  this  salt  from  uric  acid  and  ammonia  is  a 


OF   MICROSCOPIC   OBJECTS.  113 

rather  difficult  process,  and  will  not,  on  that  account,  be  de- 
scribed here ;  but  when  possessed,  a  small  quantity  of  a 
strong  solution  in  water  must  be  made,  and  a  little  placed 
on  the  slide,  and  evaporated  slowly.  Parb  of  the  salt  will 
then  be  deposited  in  circles  with  the  needle-like  crystals 
extending  from  common  centres.  They  should  then  be 
mounted  in  pure  Canada  balsam  ;  and,  when  the  best  colours 
are  wanted,  used  with  the  selenite  plate.  Of  this  class  of 
crystal,  salicine  is  a  universal  favourite,  and  can  be  easily 
procured  of  most  chemists.  The  crystals  may  be  produced 
in  two  ways  : — A  small  portion  of  the  salt  must  be  placed 
upon  the  slide,  and  a  strong  heat  applied  underneath  until 
fusion  ensues  ;  the  matter  should  then  be  evenly  and  thinly 
spread  over  the  surface.  In  a  short  time  the  crystals  will 
form,  and  are  generally  larger  than  those  procured  by  the 
following  process ;  but  the  uncertainty  is  increased  a  little 
when  fusion  is  used,  which,  however,  is  desirable  with  many 
salts.  Secondly,  make  a  saturated  solution  of  salicine, 
which  is  effected  by  boiling  one  part  of  the  salt  in  eighteen 
of  water,  and  allowing  it  to  cool.  Place  a  little  upon  the 
slide,  and  let  it  evaporate  spontaneously,  or  with  the  aid  of 
gentle  heat.  The  crystals  are  generally  uniform,  and  with 
ordinary  powers  quite  large  enough  to  make  a  beautiful 
object.  Their  circular  shape  and  gorgeous  colours — even 
without  a  selenite  plate — have  made  them  such  great 
favourites  that  there  are  few  cabinets  without  them. 

There  are  also  some  salts  which  are  crystallized  in  a  some- 
what different  manner  from  those  before  mentioned.  San- 
tonine  is  one  of  the  most  beautiful,  and  will  illustrate  my 
meaning.  Place  a  small  portion  upon  a  slide,  and  heat  over 
a  lamp  until  it  is  fused.  With  a  hot  needle  spread  the  salt 
over  the  surface  required.  As  the  slide  cools,  the  formation 
of  crystals  takes  place,  until  it  becomes  one  mass.  This 
salt  is  slightly  soluble  in  the  ordinary  balsam,  and  should 
be  mounted  in  castor  oil.  If,  however,  the  slide  is  well 
covered  under  the  thin  glass,  the  balsam  soon  becomes 
saturated,  and  very  little  injury  re;ults.  According  to  the 

I 


114-  PREPARATION   AND   MOUNTING 

temperature  daring  crystallization  the  character  of  the 
crystals  is  affected.  If  the  fused  salt  is  very  hot,  the  crystals 
run  in  straight  lines  from  a  common  centre.  If  the  heat  is 
(what  I  may  term)  medium,  the  crystals  show  concentric 
waves  of  very  decided  form.  If  the  slide  is  cool,  the  crystals, 
still  concentric,  are  exceedingly  minute.  The  most  beautiful  • 
crystals  for  the  microscopist  are  those  formed  at  a  tem- 
perature betwixt  the  second  and  third  above  mentioned,  as 
the  minute  and  wavy  forms  are  then  combined,  and  long 
feathery  crystals  are  the  result.  As  this  method  requires 
some  little  practice,  many  crystallize  the  salt  in  a  simpler 
manner,  which  I  will  give ;  but  the  variations  obtainable 
by  fusion  give  that  mode  the  precedence.  Dissolve  a  few 
grains  of  santonine  in  a  drachm  of  chloroform,  and  drop  the 
solution  upon  a  glass  slide.  Allow  the  liquid  to  evaporate, 
and  beautiful  crystals  will  be  the  result.  Mount  as  above. 

In  fear  of  being  somewhat  uninteresting  to  part  of  my 
readers,  I  feel  as  though  I  should  not  be  fulfilling  my  desire 
of  giving  every  information,  if  I  omitted  to  show  another 
method  of  crystallization,  which  a  novice  would  cast  away 
as  a  failure  before  he  had  completed  his  experiment.  Tartrate 
of  soda,  made  by  neutralizing  a  strong  solution  of  tartaric 
acid  by  the  addition  of  carbonate  of  soda,  is  spread  in  solu- 
tion over  a  glass  slide,  and  must  be  then  warmed,  but  not 
boiled.  It  must  now  be  laid  in  a  dry  place,  protected  from 
all  chance  of.  dust.  In  time — from  one  or  two  days  to  as 
many  weeks — some  of  the  slides  will  prove  beautiful  objects, 
showing  the  cross  form  surrounded  by  rays.  Some  of  these 
slides  never  crystallize,  though  I  can  find  no  reason  for  this, 
and  even  the  application  of  heat  to  these  calls  out  no  decided 
form. 

Hippuric  acid  will  be  found  most  interesting  to  those  who 
are  fond  of  beautiful  polariscopic  effects,  inasmuch  as  this 
salt  is  capable  of  giving  an  astounding  variety  in  the  forms 
of  its  crystals.  Make  a  saturated  solutio'n  in  absolute 
alcohol,  and  use  it  warm  ;  by  dropping  a  small  quantity 
from  a  warm  pipette  on  to  a  warm  slide  a  film  will  spread 


OF   MICROSCOPIC   OBJECTS.  115 

over  the  slide  and  crystals  of  a  circular  form  will  begin  to 
appear,  and  may  be  modified  by  the  atmosphere  in  which 
they  are  allowed  to  grow  ;  thus  a  moist  atmosphere  or  the 
reverse,  an  atmosphere  of  vapour  of  ammonia,  spirit,  benzole, 
or  sulphureous  fumes,  will  each,  produce  a  different  result, 
and  the  modifications  thus  produced  will  afford  food  for  very 
serious  reflection  on  the  changes  one  salt  may  be  made  to 
assume  in  contact  with  other  agents.  These  crystals  are 
best  mounted  in  castor  oil — balsam  that  is  very  liquid — 
not  balsam  in  benzole,  as  the  benzole  changes  the  character 
of  the  crystal. 

Many  new  forms  may  be  procured  by  uniting  two  totally 
different  salts  in  solution  in  certain  proportions.  This  is  a 
field  affording  new  facts  and  beauties ;  but  requires  some 
chemical  knowledge  and  much  perseverance  to  obtain  very 
valuable  results.  One  of  the  most  beautiful  I  have  met 
with  has  been  composed  of  sulphate  of  copper  and  sulphate 
of  magnesia.  The  flower-like  forms  and  uniformity  of 
crystallization  when  successful  make  it  well  worth  a  few 
failures  at  first ;  and  as  I  became  acquainted  with  some  new 
facts  in  my  frequent  trials,  I  will  give  the  preparation  of  the 
double  salt  from  the  beginning. 

Make  a  saturated  solution  of  the  two  sulphates,  combined 
in  the  proportion  of  three  parts  copper  to  one  part  mag- 
nesia, and  then  add  to  the  solution  one-tenth  of  pure  water. 
No  dust  or  other  impurities  should  have  access  to  the  slide, 
and  it  should  be  freed  from  all  traces  of  grease  by  cleaning 
immediately  before  use  with  liquor  potassse  or  ammonias.  A 
drop  of  the  solution  should  then  be  placed  upon  it,  and  by 
a  thin  glass  rod  spread  evenly  upon  the  surface.  Heat 
this  whilst  in  a  horizontal  position  until  the  salt  remains  as 
a  viscous  transparent  substance,  which  will  not  be  effected 
until  it  is  raised  to  a  high  degree.  The  slide  may  now  be 
allowed  to  cool,  and  when  this  is  accomplished,  the  flower- 
like  crystals  will  be  perceived  forming  here  and  there  upon 
the  plate.  When  these  are  at  any  stage  in  which  it  is 
wished  to  preserve  them,  a  few  seconds'  exposure  to  the  fire, 
I  2 


116  PROPAGATION   AND   MOUNTING 

as  warm  as  the  hand  can  comfortably  bear,  will  stop  the 
expansion,  when  the  portion  which  we  wish  to  mount  should 
be  cut  off  from  the  mass  of  salt  by  simply  scratching  the 
film  around,  and  pure  Canada  balsam  with  the  thin  glass 
used.  Breathing  upon  the  film,  or  allowing  the  slide  to 
become  cold  and  attract  the  moisture  from  the  atmosphere, 
will  cause  the  crystallization  to  extend,  and  sometimes 
greatly  rob  the  effect ;  so  it  is  necessary  to  mount  quickly 
when  the  desired  forms  are  obtained.  As  the  crystals  are 
very  uncertain  as  to  the  place  of  their  formation,  I  may 
here  mention  that  they  may  be  got  in  any  part  of  the  slide 
by  piercing  the  film  with  a  needle-point ;  but  in  some  degree 
this  necessarily  interferes  with  the  centre.  Into  the  cause 
of  this  we  have  no  need  to  enter  here,  and  as  it  has  been 
elsewhere  discussed,  I  can  only  give  the  above  directions,  and 
say  that  there  is  a  great  field  in  this  branch  of  study  which 
the  microscope  alone  has  opened. 

It  would  be  useless  to  enter  into  particulars  respecting  the 
various  salts  and  treatment  they  require,  as  a  great  differ- 
ence is  effected  even  by  the  strength  of  the  solution.  There 
are  some  crystals,  also,  which  are  called  forth  in  insulated 
portions,  showing  no  formation  upon  the  ground;  but  even 
when  mounted  in  any  preserving  fluid,  and  unchanged  for  a 
year,  a  new  action  seems  to  arise,  and  a  groundwork  is  pro- 
duced which  bears  little  resemblance  to  the  original  crystal. 
Sometimes  this  new  formation  adds  to  the  beauty  of  the 
slide ;  in  other  cases  the  reverse  is  the  result,  the  slide  being 
rendered  almost  worthless.  This  action,  I  believe,  frequently 
arises  from  some  liquid  being  contained  in  the  balsam  or 
other  mounting  medium  used  ;  and  this  is  rendered  the  more 
probable  by  the  crystallization  being  called  forth  in  an  hour 
after  the  balsam  diluted  with  chloroform  is  employed, 
whereas  no  change  would  have  taken  place  for  months  (if  at 
all)  had^pure  balsam  been  used. 

Sections  of  some  of  the  salts  are  very  interesting  objects ; 
but  the  method  of  procuring  these  and  their  nature  will  be 
described  in  Chapter  VI. 


OF  MICROSCOPIC  OBJECTS.  117 

Few  objects  are  more  beautiful  with  polarized  light 
than  young  oysters.  Good  colours  and  a  decided  cross 
are  given  by  them  when  well  prepared.  The  following  is 
the  method  pursued  by  Mr.  Henry  Lee : — Having  found  a 
"  black-sick  "  oyster  (to  use  the  dredgemen's  term),  the  spawn 
of  which  is  quite  mature  and  ready  for  extrusion,  pour  off 
from  the  shell  the  dark  slate-coloured  fluid  into  a  long 
narrow  two-ounce  phial ;  fill  up  the  bottle  with  distilled 
water ;  shake  it  gently ;  allow  the  deposit  to  settle,  and 
change  the  water  two  or  three  times,  repeating  the  agitation 
to  get  rid  of  the  salt.  Then  substitute  for  the  water  liquor 
potassee,  diluted  with  equal  quantity  of  distilled  water. 
Allow  the  young  oysters  to  remain  in  this  for  two  days, 
agitating  occasionally  ;  and  aa  often  as  the  liquid  becomes 
discoloured  pour  it  off,  and  renew  the  same  until  no  colour 
is  given  off  and  the  shells  are  seen  to  be  thoroughly  cleansed 
from  all  animal  matter  by  their  sinking  freely  and  rapidly 
to  the  bottom.  When  this  stage  is  arrived  at,  stop  the 
process,  that  the  two  valves  of  the  shells  may  not  be  sepa- 
rated by  the  destruction  of  the  hinge.  Wash  repeatedly  in 
distilled  water,  to  remove  all  trace  of  alkali,  and  finally  wash 
and  preserve  the  shells  in  a  little  rectified  spirits  of  wine 
(not  methylated  spirit).  These  objects  are  frequently 
mounted  in  balsam,  to  increase  their  transparency  for  the 
polariscope,  but  where  they  are  sufficiently  clear  they  may 
be  mounted  dry  like  the  foraminifera. 

The  scales  of  various  fish  have  been  before  mentioned 
as  mounted  dry ;  when,  however,  they  are  required  for 
polarizing  objects,  they  are  generally  mounted  in  balsam, 
and  some  few  in  liquid.  The  former  method  will  be  con- 
sidered here. 

The  eel  affords  a  beautiful  object  for  this  purpose.  The 
scales  are  covered  by  a  thin  skin,  which  may  be  slightly 
raised  with  a  knife  and  then  torn  off,  in  the  same  manner 
as  the  covering  of  the  geranium  and  other  petals,  described 
in  Chapter  III.  The  required  portion  may  then  be  removed ; 
or  if  a  piece  of  skin  can  be  procured  as  stripped  off  in. 


118  rBEPAUATION   AND   MOUNTING 

cooking,  the  scales  may  be  easily  taken  from  the  inner 
surface.  They  must  then  be  washed  and  thoroughly 
cleaned.  After  drying,  soak  for  a  day  in  turpentine,  and 
mount  in  the  ordinary  manner  with  balsam.  This  is  a 
good  polarizing  object ;  but  the  interest,  and  I  think  the 
beauty,  is  increased  by  procuring  a  piece  of  eel's  skin  with 
the  scales  in  situ,  washing  and  drying  under  pressure,  and 
mounting  in  balsam  as  before.  The  arrangement  of  the 
scales  produces  beautiful  "  waves "  of  colour,  which  are 
quite  soothing  to  the  eye  after  examining  some  of  the  very 
gorgeous  salts. 

There  are  many  scales  of  fish  which,  are  good  subjects  for 
the  polariscope  when  mounted  in  balsam ;  but  as  they  re- 
quire no  particular  treatment,  they  need  no  mention  by- 
name. 

Among  hairs  we  find  some  which  are  beautiful  when 
mounted  in  balsam  and  examined  by  polarized  light.  Some, 
when  wanted  as  common  objects,  are  always  used  dry,  as 
before  mentioned  ;  but  if  they  are  intended  to  be  shown  as 
polarizing  object?,  they  must  be  placed  in  some  medium. 
The  Micrographic  Dictionary  mentions  a  mode  of  making 
an  interesting  object  by  plaiting  two  series  of  white  horse- 
hairs at  an  angle,  mounting  in  balsam,  and  using  with  the 
polariscope.  All  hairs,  however,  must  be  steeped  in  tur- 
pentine for  a  short  time  before  mounting,  as  they  will  thus 
be  rendered  cleaner  and  more  transparent.  When  this  is 
done,  there  is  no  difficulty  in  mounting  them. 

Many  of  the  "  tongues "  of  fresh-water  and  marine 
mqllusca  are  deeply  interesting  and  most  beautiful  objects 
when  examined  by  polarized  light.  As  these  are  usually 
mounted  in  balsam,  I  mention  them  in  this  place ;  but  as 
they  must  be  removed  from  the  animals  by  dissection, 
particulars  respecting  them  will  not  be  entered  into  until 
we  come  to  the  part  in  which  that  operation  is  described 
(Chapter  VI.). 

The  manner  of  preparing  and  mounting  many  of  the 
Polyzoa  and  Zoophytes  has  been  before  described ;  but  any 


OF  MICROSCOPIC  OBJECTS.  119 

notice  of  polarizing  objects  would  be  incomplete  without 
some  allusion  to  them.  A  small  piece  of  the  Flustra 
avicularis,  well  prepared,  is  beautiful  when  examined  in 
this  manner.  No  selenite  is  needed,  and  yet  the  colours 
are  truly  gorgeous.  It  is  often  met  with  upon  shells  and 
zoophytes  of  a  large  size,  and  will  well  repay  the  trouble 
of  searching  for.  Many  of  the  Sertularidos  are  very  beau- 
tiful with  polarized  light,  and,  indeed,  no  ramble  upon  the 
seaside  need  be  fruitless  in  this  direction. 

The  different  starches  are  quite  a  study  in  themselves, 
and  are  peculiarly  connected  with  polarized  light.  They 
are  found  in  the  cellular  tissue  of  almost  every  plant  in 
small  white  grains,  which,  vary  considerably  in  size ;  that 
from  the  potato  averages  one- three-hundredth  of  an  inch  in 
diameter,  and  that  from  arrow-root  about  one-six-hundredth. 
To  procure  starch  from  any  plant,  the  texture  must  first  be 
broken  up  or  ground  coarsely ;  the  mass  of  matter  must  be 
then  well  washed  in  gently-flowing  water,  and,  as  all  starch 
is  totally  insoluble  in  cold  water,  the  grains  are  carried  off 
by  the  current  and  deposited  where  this  is  stayed.  In  pro- 
curing it  from  the  potato,  as  well  as  many  other  vegetables, 
it  is  but  necessary  to  reduce  the  substance  to  a  coarse  pulp 
by  the  aid  of  a  culinary  grater ;  the  pulp  should  then  be 
well  agitated  in  water,  and  allowed  to  rest  a  ehort  time, 
when  the  starch  will  be  found  at  the  bottom,  its  lighter 
colour  rendering  it  easily  distinguishable  from  the  pulp.  It 
should,  however,  be  washed  through  two  or  three  waters  to 
render  it  perfectly  clean. 

These  grains  have  no  crystalline  structure,  but  present  a 
very  peculiar  appearance  when  examined  with  polarized 
light.  Each  grain  shows  a  dark  cross  whose  lines  meet  at 
the  point  where  it  was  attached  to  the  plant,  called  the 
hilum.  Bound  the  grain  also  a  series  of  lines  is  seen,  as 
though  it  were  put  together  in  plates.  This  is  more  dis- 
tinctly visible  in  some  kinds  than  others. 

As  to  the  mounting  of  these  starches  there  is  little  to  be 
said.  If  the  grains  are  laid  upon  the  slide,  and  as  small  a 


120  PREPARATION   AND  MOUNTING 

portion  as  possible  of  the  balsam  diluted  with  turpentine, 
as  before  mentioned,  be  applied,  they  will  cling  to  the  glass 
and  allow  the  pure  balsam  to  flow  readily  over  them  with- 
out being  so  liable  to  imprison  air-bubbles  when  the  thin 
glass  is  put  upon  them. 

The  raphides,  wnich  were  fully  described  in  Chapter  III., 
when  required  for  use  with  polarized  light,  must  be  mounted 
in  balsam,  and  many  are- found  which  give  beautiful  colours. 
They  require  no  peculiar  treatment,  but  must  be  washed 
quite  clean  before  putting  up.  But  in  order  to  understand 
anything  of  the  natural  arrangement  of  raphides,  it  is 
necessary  to  mount  certain  parts  of  plants  with  these  objects 
in  situ.  The  most  common  is  the  coating  of  the  onion, 
which  must  be  soaked  some  time  in  turpentine  or  benzole, 
in  order  to  render  it  transparent,  and  must  then  be  mounted 
in  balsam,  as  before  said.  We  shall  then  be  able  to  obtain 
such  colours  by  the  aid  of  polarized  light,  that  the  rapliides 
are  shown  in  wonderful  distinctness,  and  somewhat  of  their 
nature  will  be  perceived. 

There  is  one  class  of  objects  for  the  polariscope  which 
differs  in  preparation  from  any  we  have  yet  considered,  and 
affords  very  beautiful  specimens.  Some  of  the  plants,  in- 
cluding many  of  the  grasses  and  the  Equisetacese  (i.e.  horse- 
tails), contain  so  large  a  quantity  of  silica,  that  when  the 
vegetable  and  other  perishable  parts  are  removed,  a  skeleton 
of  wonderful  perfection  remains.  This  skeleton  must  be 
mounted  in  balsam,  the  method  of  performing  which  will 
now  be  considered. 

Sometimes  the  cuticle  of  the  equisetum  is  removed  from 
the  plant,  others  dry  the  stem  under  pressure,  whilst  the 
grasses,  of  course,  require  no  such  preparation.  They  should 
then  be  immersed  in  strong  nitric  acid  and  boiled  for  a 
short  time ;  an  effervescence  will  go  on  as  the  organic  matter 
is  decomposed,  and  when  this  has  ceased,  more  acid  should 
be  added.  At  this  point  the  modes  of  treatment  differ ; 
some  remove  the  object  from  the  acid  and  wash,  and  having 


OF  MICROSCOPIC  OBJECTS.  121 

dried,  burn  it  upon  thin  glass  until  all  appears  white,  when 
it  must  be  carefully  mounted  in  balsam.  I  think,  however, 
it  is  better  to  leave  it  in  strong  acid  until  all  the  substance, 
except  the  required  portion,  is  removed ;  but  this  will  take 
a  length  of  time,  varying  according  to  the  mass  of  tha 
plant.  Of  course,  when  this  latter  method  is  used,  the 
skeleton  must  be  washed  from  the  acid,  &c.,  before  being 
mounted  in  balsam. 

These  siliceous  cuticles  are  readily  found.  The  straws  of 
most  of  the  cereals,  wheat,  oat,  &c. ;  the  husks,  also,  of  some 
of  these;  many  canes;  the  equisetum,  as  before  described; 
and  some  of  the  grasses.  Many  of  these  are  everywhere 
procurable,  so  that  the  student  can  never  want  material  for 
a  splendid  object  for  the  polariscope. 

la  Chapter  III.  the  scales  (or  hairs)  which  are  often  found 
upon  the  leaves  of  plants  were  mentioned  as  beautiful  objects 
when  mounted  dry ;  but  some  of  these  when  detached  from 
the  leaf — which  is  easily  done  by  gently  scraping  it,  when 
dried,  with  a  knife — present  brilliant  starlike  and  other 
forms,  if  mounted  in  balsam  and  used  with  the  polariscope. 
There  is  a  little  danger,  when  placing  the  thin  glass  upon 
the  balsam,  of  forcing  out  the  scales  in  the  wave  of  matter 
which  is  always  ejected;  this  may  be  overcome  by  applying 
to  the  slide,  previously  to  placing  the  objects  upon  it,  an 
extremely  thin  covering  of  balsam  diluted  with  turpentine 
as  before  mentioned,  letting  it  dry  more  or  less  with  the 
objects  placed  in  it,  and  then,  after  the  addition  of  a  little 
more  balsam,  putting  the  cover  on,  and  thus  giving  them 
every  chance  of  adherence ;  or  by  using  the  balsam  with 
chloroform,  as  before  noticed.  This  method  is  peculiarly 
successful  in  cases  where  it  is  desired  to  arrange  several 
objects  symmetrically  on  a  slide,  and  to  obviate  their  sub- 
sequent disturbance  by  placing  the  cover  on.  T)'pe  slides 
with  several  parts  of  an  insect  displaced  upon  them,  scales 
of  fish,  or  of  plants,  &c.,  may  thus  be  shown,  so  that  the 
number  of  slides  may  by  this  plan  be  seriously  diminished. 


122  PREPARATION   AND   MOUNTING 

These  scales  are  much  more  abundant  than  was  formerly 
supposed,  and  new  specimens  are  discovered  daily ;  so  that 
the  student  should  always  be  on  the  look-out  for  them  in 
his  researches  in  the  vegetable  world. 

Most  classes  of  objects,  and  the  treatment  they  require 
when  mounting  them  in  balsam,  have  now  been  considered. 
The  next  chapter  will  be  devoted  to  preservative  liquids, 
and  the  best  method  of  using  them. 


OF   MICROSCOPIC   OBJECTS.  123 


CHAPTER    V. 

PRESERVATIVE   LIQUIDS,  ETC.,   PARTICULARLY  WHERE   CELLS 
ARE   USED. 

THERE  are  many  objects  which  would  lose  all  their  distinc- 
tive peculiarities  if  allowed  to  become  dry,  especially  those 
belonging  to  the  fresh-water  Algas,  many  animal  tissues, 
and  most  of  the  very  delicate  animal  and  vegetable  sub- 
stances in  which  structure  is  to  be  shown.  These  must  be 
preserved  by  immersion  in  some  fluid ;  but  it  is  evident  that 
the  fluid  must  be  suited  to  the  kind  of  matter  which  it  is 
intended  to  preserve.  As  it  often  requires  much  study  and 
trouble  to  obtain  microscopic  objects  of  this  class,  it  is  well 
that  their  presentation  should  be  rendered  as  perfect  as 
possible ;  and  for  this  reason  the  CELLS,  or  receptacles  of  the 
fluids,  should  be  so  closed  that  all  possibility  of  escape 
should  be  prevented.  The  accomplishment  of  this  is  not  so 
easy  a  matter  as  it  might  appear  to  the  inexperienced. 

Before  giving  any  directions  as  to  the  manipulation 
required  in  mounting  the  objects,  we  must  consider  the 
different  liquids  arid  cells  which  are  requisite  for  their  pre- 
servation. Of  the  former  there  are  a  great  number,  of  which 
the  principal  may  be  mentioned. 

DISTILLED  WATER,  is  strongly  recommended  by  many  for 
Diatomaceaa  and  other  Protophytes.  It  has  been,  however, 
stated  that  confervoid  growths  often  disturb  the  clearness 
of  the  liquid,  and  on  this  account  various  additions  are  made 
to  it.  A  lump  of  camphor  is  often  left  in  the  bottle,  so  that 
the  water  may  dissolve  as  much  as  possible.  One  grain  of 
bay  salt  and  one  of  alum  are  added  to  each  ounce  of  water; 
or  a  drop  or  two  of  creosote  shaken  up  with  an  ounce  of 
•water,  which  should  be  afterwards  filtered.  These  additions 


12i  PREPARATION   AND   MOUNTING 

are  often  made ;  perhaps  each  of  them  good  for  certain 
objects. 

GLYCERINE. — Some  affirm  this  to  be  one  of  the  best  pre- 
servative liquids,  especially  for  vegetable  objects;  but  others 
think  that  it  is  much  better  when  diluted  with  two  parts  of 
camphor-water,  prepared  as  above.*  Mr.  A.  E.  Verrill,  of 
Yale  College,  U.S.,  says  glycerine  .preserves  the  natural 
colours  of  marine  animals ;  and  the  only  precaution  to  be 
taken  is  to  use  very  heavy  glycerine,  and  to  keep  up  the 
strength  by  transferring  the  specimens  to  new  as  soon  as 
they  have  given  out  water  enough  to  weaken  it  much,  re- 
peating the  transfer  till  all  the  water  is  removed  before 
finally  mounting  on  the  slide. 

GLYCERINE  AND  GUM. — This  is  also  believed  to  be  a  very 
good  liquid  for  vegetable  tissues,  and  is  thus  prepared  : — • 

Pare  gum-arabic...     1     oz. 

Glycerine     1     „ 

Water  (distilled)...     1     „ 

Arsenious  acid    ...     1|  grain. 

Dissolve  the  arsenious  acid  in  the  cold  water,  then  the  gum, 
add  the  glycerine,  and  mix  without  bubbles. 

Dr.  Carpenter  states  that  the  proportions  used  ultimately 
by  the  late  Mr.  Farrants  are : — 

Picked  gum-arabic  ...  4  parts  by  weight. 
Distilled  water  (cold)..  4      „  „ 

Glycerine 2      „  „ 

Thus  he  now  omits  the  arsenious  acid,  but  places  in  the 
solution  (which  should  be  kept  in  a  bottle  with  glass  stop- 

*  Dr.  Carpenter  says  : — "Glycerine  has  a  solvent  power  for  carbo- 
nate of  lirne,  and  should  not  be  employed  when  the  object  contains 
any  calcareous  structure.  In  ignorance  of  this  fact,  the  author  (Dr. 
C.)  employed  glycerine  to  preserve  a  number  of  remarkably  fine  speci- 
mens of  the  pentacrinoid  larva  of  the  Comatula,  whose  colours  he  was 
anxious  to  retain  ;  and  was  extremely  vexed  to  find,  when  about  to 
mount  them,  that  their  calcareous  skeletons  had  so  entirely  disap- 
peared, that  the  specimens  were  completely  ruined." 


OF   3IICEOSCOPIC   OBJECTS.  125 

per)  a  small  piece  of  camphor.  This  requires  no  cell,  as  the 
adhesive  power  is  sufficient. 

DEANE'S  COMPOUND. — This  is  usually  deemed  about  the 
best  medium  for  preserving  Algae,  mosses,  &c.,  and  is  thus 
prepared : — Soak  1  oz.  of  best  gelatine  in  4  oz.  of  water 
until  the  gelatine  becomes  soft,  when  5  oz.  of  honey  heated 
to  boiling  point  are  added;  boil  the  mixture,  and  when  it 
has  cooled,  but  not  enough  to  become  stiff,  add  %  oz.  recti- 
fied spirit  with  which  5  or  6  drops  of  creosote  have  been 
well  mixed,  and  filter  the  whole  through  fine  flannel.  This 
compound  when  cold  forms  a  stiff  jelly,  the  use  of  which 
will  be  described  elsewhere. 

GLYCERINE  JELLY. — This  mixture  closely  resembles  the 
above,  but  as  the  composition  differs  a  little  it  may  be  men- 
tioned here.  It  is  strongly  recommended  by  Mr.  Lawrance 
in  the  Microscopic  Journal,  where  he  states  "  that  the 
beautiful  green  of  some  mosses  mounted  two  years  ago,  is  still 
as  fresh  as  on  the  day  they  were  gathered ;"  and  that  this 
is  the  only  medium  he  knows  which  will  preserve  the  natural 
colour  of  vegetable  substances.  He  takes  a  quantity  of 
Nelson's  gelatine,  soaks  it  for  two  or  three  hours  in  cold 
water,  pours  off  the  superfluous  water,  and  heats  the  soaked 
gelatine  until  melted.  To  each  fluid  ounce  of  the  gelatine, 
whilst  it  is  fluid  but  cool,  he  adds  a  fluid  drachm  of  the 
white  of  an  egg.  He  then  boils  this  until  the  albumen 
coagulates  and  the  gelatine  is  quite  clear,  when  it  is  to  be 
filtered  through  fine  flannel,  and  to  each  ounce  of  the  clari- 
fied solution  add  6  drachms  of  a  mixture  composed  one  part 
of  glycerine  to  two  parts  of  camphor-water. 

At  the  Academy  of  Natural  Sciences  of  Philadelphia, 
Mr.  TV.  H.  Walmsley  stated,  that,  owing  to  the  heat  of  that 
climate,  the  above  formula  for  glycerine  jelly  was  not  satis- 
factory, and  recommended  the  following  : — Take  one  pack- 
age of  Cox's  gelatine,  wash  repeatedly  in  cold  water ;  allow 
it  to  soak  in  water  sufficient  to  cover  it  for  an  hour  or  two, 
add  one  pint  of  boiling  water,  and  boil  ten  or  fifteen 
minutes.  Remove,  and  when  cool  but  still  fluid,  add  the 


126  PREPARATION   AND   MOUNTING 

white  of  an  egg,  well  beaten,  and  agaiu  boil,  until  the  albu- 
men coagulates.  Strain  whilst  hot  through  flannel,  and 
add  an  equal  portion  by  measurement  of  Bowyer's  pure 
glycerine,  and  fifty  drops  of  carbolic  acid  in  solution ;  boil 
again  for  ten  or  fifteen  minutes,  and  again  strain  through 
flannel,  place  in  a  water-bath  and  evaporate  to  about  one- 
half,  then  filter  into  two  or  more  broad-mouthed  vials.  (Cotton 
is  the  best  filtering  medium.)  The  use  of  this  in  mounting 
is  the  same  as  Mr.  Lawrance's,  elsewhere  described. 

GOADBY'S  FLUID. — This  is  much  used  in  the  preservation 
of  animal  objects ;  and  seldom,  if  ever,  acts  upon  the  colours. 
It  is  thus  prepared: — Bay  salt,  4  oz.;  alum,  2  oz.;  corrosive 
sublimate,  4  grains.  Dissolve  these  in  two  quarts  of  boiling 
water,  and  filter.  For  delicate  preparations  some  recom- 
mend that  this  mixture  be  reduced  by  the  addition  of  an 
equal  quantity  of  water ;  but  where  there  is  bone  or  shell  in 
the  object,  the  above  acts  injuriously  upon  it,  in  which  case 
this  fluid  may  be  used: — Bay  salt,  8  oz. ;  corrosive  subli- 
mate, 2  grains ;  water,  1  quart. 

THWAITES'S  LIQUID. — This  is  recommended  for  the  preser- 
vation of  Algae,  &c.,  as  having  little  or  no  action  on  the 
colour,  and  is  thus  prepared: — Take  one  part  of  rectified 
spirit,  add  drops  of  creosote  enough  to  saturate  it;  to  this 
add  sixteen  parts  of  distilled  water  and  a  little  prepared 
chalk,  and  filter.  When  filtered,  mix  with  an  equal  quantity 
of  camphor-water  (as  before  mentioned),  and  strain  through 
fine  muslin  before  using. 

.  CHLORIDE  OF  ZINC  SOLUTION. — In  the  Micrographic  Dic- 
tionary this  is  stated  to  be  "  perhaps  the  best  preservative 
known  for  animal  tissues."  Persons  of  great  experience, 
however,  have  given  a  very  different  opinion ;  -but  it  is  cer- 
tainly very  useful  in  many  cases  where  a  small  degree  of 
coagulating  action  is  not  injurious.  It  is  used  of  strengths 
varying  according  to  the  softness  of  the  parts  to  be  pre- 
served ;  the  average  being  20  grains  of  the  fused  chloride  to 
1  oz.  of  distilled  water.  To  keep  this  liquid,  a  lump  t»f  cam- 
phor may  be  left  floating  in  the  bottle.  I  have  heard  com- 


OF   MICROSCOPIC   OBJECTS.  127 

plaints  that  this  mixture  becomes  turbid  with  keeping;  but 

1  think  this  must  only  be  the  case  when  some  impurity  has 
got  into  the  bottle. 

CARBOLIC  ACID.* — The  addition  of  a  few  drops  of  this  to 
distilled  water  prevents  the  growth  of  interfering  substances 
which  would  take  place  if  pure  water  alone  were  used,  and 
is  therefore  valuable  as  a  preservative  fluid.  The  same 
solution  also  is  convenient,  as  it  instantly  kills  infusoria,  and 
almost  everything  that  has  life;  and,  indeed,  is  useful  in 
the  student's  gathering-bottles  for  the  same  reason.  It  is 
very  highly  spoken  of  as  forming  one  of  the  constituents  in 
the  following  formula  for  use  in  mounting  soft  animal 
textures : — • 

Arsenious  acid,  20  parts. 
Crystallized  carbolic  acid,  10  parts. 
Alcohol,  300  parts. 
Distilled  water,  700  parts. 

The  Rev.  W.  VV.  Spicer,  in  his  translation  of  Johann 
Nave's  work  on  Alga?,  recommends  the  following  fluid  for 
their  preservation  : — Pure  alcohol,  3  parts  ;  distilled  water, 

2  parts;  glycerine,    1    part.'   If  the   desmid  or  other  alga 
be  placed  in  this  fluid  in  a  cell,  and  not  covered  by  a  glass 
for  a  time,  the  water  and  alcohol  will  evaporate  slowly,  and 
the  mixture  will  become  more  dense  in  proportion,  but  quite 
gradually,  and  therefore  without  any   destructive  influence 
on  the  object.     During  this   operation,  water  is  withdrawn 
from  the   frustule,  and  the  glycerine,  which  is  not  volatile, 
takes  its  place  without  causing  any  distortion  of  the  object. 

CASTOB  OIL. — This  is  a  very  useful  preservative  for 
crystals  and  other  objpcts.  Many  salts  are  quite  destroyed 
when  Canada  balsam  is  used  with  them;  but  very  few  are 
acted  upon  by  this  oil.  To  use  it,  it  must  be  dropped  in 
(sufficient  quantity  to  cover  the  crystal  or  object  to  be 

*  Dr.  Grace  Calvert  stated  at  a  meeting  of  the  British  Association, 
that  after  careful  experiments  he  finds  carbolic  acid  "  prevents  the 
development  of  protoplasmic  and  fungoid  life." 


128  PREPABATION    AXD  MOTJKTIXG 

preserved  with  a  thin  coating  of  oil.  It  may  be  necessary 
sometimes  to  spread  it  with  a  needle  or  other  instrument. 
The  thin  glass  should  then  be  carefully  placed  upon  it,  so 
that  all  air  may  be  excluded ;  and  should  any  oil  be  forced 
out,  owing  to  the  quantity  used  being  too  great,  it  must 
be  removed  with  blotting-paper.  When  the  edge  of  the 
thin  glass  cover  and  the  surrounding  parts  of  the  slide  are 
as  clean  as  possible,  a  coating  of  sealing-wax  varnish  or 
liquid  glue  must  be  applied  and  allowed  to  dry.  A  second 
or  even  a  third  coating  may  be  required,  but  not  before  the 
previous  cover  is  quite  dry.  These  varnishes,  however,  are 
very  brittle,  and  it  is  much  safer,  as  a  finish,  to  use  one  of 
the  tougher  cements — gold-size,  for  instance — which  will 
render  it  doubly  secure. 

The  above  are  the  principal  liquids,  &c.,  nsed  for  pre- 
serving objects  in  cells.  The  different  cells  may  be  here 
mentioned  ;  and  it  is  recommended  that  these  should  always 
be  kept  some  time  before  use  in  order  that  the  cement  may 
become  perfectly  dry ;  and  care  must  be  taken  that  no 
cement  be  used  on  which  the  preservative  liquid  employed 
has  any  action  whatever. 

CEMENT  CELLS. — "Where  the  object  is  not  very  thick,  this 
kind  of  cell  is  generally  used.  They  are  easily  made  with 
the  turntable  before  described  ;  but  when  the  objects  to  be 
preserved  are  very  minute,  these  cells  need  not  be  much 
deeper  than  the  ordinary  circle  of  cement  on  the  slide. 
When,  however,  a  comparatively  great  depth  is  required,  it 
is  sometimes  necessary  to  make  the  wall  of  the  cell  as  deep 
as  possible,  then  allow  it  to  dry  and  make  another  additiou. 
Of  these  cements  gold-size  is  one  of  the  most  trustworthy, 
and  may  be  readily  used  for  the  shallow  cells.  The  as- 
phaltum  and  india-rubber,  before  noticed,  I  have  found  very 
durable  when  well  baked,  and  exceedingly  pleasant  to  work 
with.  It  may  be  used  of  such  a  thickness  as  to  give  space 
for  tolerably  large  objects.  Black  japan  also  is  much  used. 
Many  cements,  however,  which  are  recommended  by  some 
writers,  are  worse  than  useless,  owing  to  the  brittleness  which 


OF   MICROSCOPIC   OBJECTS.  129 

renders  their  durability  uncertain,  as  sealing-wax,  varnish, 
liquid-glue,  &c.  Dr.  Bastian  says  the  best  cement  for  liquid 
cells  is  one,  much  used  in  Germany,  made  by  adding  a 
considerable  quantity  of  nitrate  of  bismuth  to  a  solution  of 
gum  mastic  in  chloroform.  It  can  be  procured  at  almost 
any  optician's. 

The  student  may  feel  himself  at  a  loss  in  choosing  the 
cement  which  will  give  him  the  safest  cells,  many  of  them 
becoming  partially  or  wholly  dry  in  a  year  or  two,  as  stated 
in  another  place.  I  can  only  give  him  a  few  general  direc- 
tions, and  he  must  then  use  his  own  judgment.  Of  course 
it  would  be  lost  labour  to  employ  any  cement  upon  which 
the  preservative  liquid  has  any  action  whatever.  It  is  also 
a  good  rule  to  avoid  those  in  whose  composition  there  are 
any  particles  which  do  not  become  a  thorough  and  intimate 
portion,  as  these  unreduced  fragments  will  almost  certainly, 
sooner  or  later,  prepare  a  road  by  which  the  liquid  will 
escape  ;  and,  lastly,  whatever  cement  he  uses,  the  cells  are 
always  better  when  they  have  been  kept  a  short  time  before 
use. 

GUTTA-PJERCHA  EINGS  have  been  recommended  by  some, 
as  affording  every  facility  for  the  manufacture  of  cells  for 
liquids ;  but  they  cannot  be  recommended,  as,  after  a  certain 
length  of  time,  they  become  so  brittle  as  to  afford  no  safe- 
guard against  ordinary  accidents.  Some  have  also  used 
india-rubber  bands  thickly  coated  with  various  varnishes ; 
but  these  I  consider  less  trust- worthy  than  gutta- 
percha,  as  they  become  thoroughly  rotten  in  ordinary 
use  after  a  short  probation. 

Often  the  cells  must  necessarily  be  of  a  large  size,  and 
for  this  reason  are  made  by  taking  four  strips  of  glass  of  the 
thickness  and  depth  required,  and  grinding  the  places  where 
these  are  to  meet  with  emery,  so  as  to  form  a  slightly 
roughened  but  flat  edge.  The  glass  strip  must  also  be 
ground  on  the  side  where  it  meets  the  plate,  and  each  piece 
cemented  with  the  marine-glue  mentioned  in  Chapter  II  in 
the  following  manner  : — On  that  part  of  the  glass  to  which 

K 


130  PREPARATION   AND   MOUNTING 

another  piece  is  to  be  attached  should  be  laid  thin  strips  of 
the  glue ;  both  pieces  must  then  be  heated  upon  a  small 
brass  table,  with  the  aid  of  the  spirit-lamp,  until  the  strips 
become  melted ;  the  small  piece  is  then  to  be  taken  up  and 
placed  upon  the  spot  to  which  it  is  to  be  attached,  and  so 
on  until  the  cell  is  completed.  It  will  be  found  necessary  to 
spread  the  glue  over  the  surface  required  with  a  needle  or 
some  other  instrument,  so  that  an  unbroken  line  may  be 
presented  to  the  wall  of  the  cell,  and  no  bubbles  formed. 
Too  great  a  heat  will  burn  the  marine-glue,  and  render  it 
brittle ;  care  must  be  therefore  taken  to  avoid  this. 

When  shallow  cells  are  required,  those  which  are  made 
by  grinding  a  concavity  in  the  middle  of  an  ordinary  slide 
will  be  found  very  convenient.  The  concavities  are  cut  both 
circular  and  oblong ;  and  the  surface  being  flat,  the  cover  is 
easily  fastened  upon  it.  These  are  now  cheap,  and  are  very 
safe  as  to  leakage.  It  is  a  very  great  improvement,  where 
it  can  be  done,  to  turn  a  shallow  ring  outside  the  concavity 
of  the  slide,  but  close  to  it.  This  prevents  the  cement  with 
which  the  cover  is  fastened  from  running  in. 

Circular  cells  with  a  flat  bottom  used  to  be  made  by 
drilling  a  hole  through  glass  of  the  required  thickness,  and 
fixing  this  upon  an  ordinary  slide  with  marine-glue ;  but 
the  danger  of  breakage  and  the  labour  were  so  great  that 
this  method  is  seldom  used  now,  and,  indeed,  the  rings  about 
to  be  mentioned  do  away  with  all  necessity  for  it. 

GLASS  RINGS. — Where  any  depth  is  required,  no  method 
of  making  a  cell  for  liquids  is  so  convenient  as  the  use  of 
glass  rings,  which  are  now  easily  and  cheaply  procurable. 
They  are  made  of  almost  every  size  and  depth,  and,  except 
in  very  extraordinary  cases,  the  necessity  for  building  cells 
is  completely  obviated.  These  rings  have  both  edges  left 
rough,  and  consequently  adhere  very  well  to  the  slide,  this 
adherence  being  generally  accomplished  by  the  aid  of 
marine-glue,  as  before  noticed  with  the  glass  cells.  Gold- 
size  has  been  occasionally  used  for  this  purpose ;  and  the 
adherence,  even  with  liquid  in  the  cell,  I  have  always  found 


OF  MICROSCOPIC  OBJECTS.  131 

to  be  perfect.  This  method  has  the  advantage  of  requiring 
no  heat,  but  the  gold-size  must  be  perfectly  dry,  and  the 
ring  must  have  been  fixed  upon  the  slide  some  time  before 
use.  Canada  balsam  has  also  been  used  for  the  same 
purpose,  but  cannot  be  recommended,  as,  when  it  is  perfectly 
dry,  it  becomes  so  brittle  as  to  bear  no  shock  to  which  the 
slide  may  be  ordinarily  exposed. 

IRON  BINGS. — Many  have  worked  with  these,  having 
taken  care  to  varnish  thoroughly  before  using  with  any 
preservative  liquid  ;  but  they  are  always  untrustworthy,  as 
they  can  never  be  guaranteed  against  the  action  of  some  salt 
in  the  liquid  used.  They  can  be  procured  beautifully  made, 
and  for  dry  cells  cannot  be  surpassed.  Zinc  and  pure  tin 
rings  may  also  be  procured,  and  are  excellent,  especially  the 
latter. 

VULCANITE. — This  substance  is  a  great  favourite  with 
some  of  our  working  microscopists,  as  it  is  very  slightly  in- 
fluenced by  change  of  temperature.  But  my  own  opinion  is 
that  a  glass  cell  is  the  safest  and  most  satisfactory  re- 
ceptacle for  any  object  in  liquid,  and  if  carefully  prepared 
will  not  deceive  the  operator. 

These  are  the  cells  which  are  mostly  used  in  this  branch 
of  microscopic  mounting.  The  mode  of  using  them,  and  the 
different  treatment  which  certain  objects  require  when  in- 
tended to  be  preserved  in  the  before-mentioned  liquids,  may 
now  be  inquired  into. 

I  may  mention,  however,  that  this  class  of  objects  is 
looked  upon  by  many  with  great  mistrust,  owing  to  the 
danger  there  is  of  bubbles  arising  in  the  cells  after  the 
mounting  has  been  completed,  even  for  years.  I  know  some 
excellent  microscopists  who  exclude  all  objects  in  cells  and 
preservative  liquids  from  their  cabinets,  because  they  say 
that  eventually  almost  all  become  dry  and  worthless ;  and 
this  is  no  matter  of  surprise,  for  many  of  them  do  really 
become  so.  Perhaps  this  is  owing  to  the  slides  being  sold 
before  they  could  possibly  be  thoroughly  dry.  As  to  the 
air-bubbles,  I  shall  have  sometfting  to  say  presently. 
K  2 


132  PKEPAKATION  AND  MOUNTING 

We  will  now  suppose  the  cell  employed  has  been  made 
by  placing  a  glass  ring  upon  the  slide  with  marine-glne  or 
gold-size,  and  is  quite  dry.  Around  the  edge  of  the  cleaned 
thin  glass  which  is  to  cover  it,  I  trace  with  a  camel-hair 
pencil  a  ring  of  gold-size,  and  also  around  the  edge  of  the 
cell  to  which  it  is  to  adhere.  Dr.  Carpenter  objects  to  this, 
as  rendering  the  later  applications  of  the  gold-size  liable  to 
"  run  in."  All  danger  of  this,  however,  is  completely  ob- 
viated by  leaving  the  slide  and  cover  for  awhile  until  the 
cement  becomes  partially  fixed,  but  still  adhesive  enough 
to  perform  its  function  (Chapter  III.).  With  many  slides 
this  is  not  accomplished  in  less  than  twenty-four  hours,  even 
if  left  two  or  three  days  no  injury  whatever  ensues ;  but 
with  other  kinds  an  hour  is  too  long  to  leave  the  exposed 
cement,  so  that  the  operator  must  use  his  own  discretion. 
It  is  not  always  necessary  to  size  the  edge  of  the  cover, 
since  perfect  adhesion  may  in  many  cases  be  secured  with- 
out it,  and  it  is  always  best  to  use  the  least  quantity  of 
cement  that  will  answer,  as  it  will  then  be  less  likely  to  run 
in.  The  liquid  required  may  be  drawn  up  by  the  month 
into  the  pointed  tube  mentioned  in  Chapter  II.,  and  then 
transferred  to  the  cell.  In  the  various  books  of  instruction, 
the  object  is  now  to  be  placed  in  the  cell ;  this,  however,  I 
think  a  great  mistake,  as  another  process  is  absolutely 
necessary  before  we  advance  so  far.  The  cell,  full  of  liquid, 
must  be  placed  under  the  receiver  of  an  air-pump,  and  the 
air  withdrawn.  Almost  immediately  it  will  be  perceived 
that  the  bottom  and  sides  of  the  cell  are  covered  with  minute 
bubbles,  which  are  formed  by  the  air  that  is  held  in  sus- 
pension by  the  liquid.  The  slide  may  now  be  removed,  and 
the  bubbles  may  require  the  aid  of  a  needle  or  other  point 
to  displace  them,  so  obstinately  do  they  adhere  to  the 
surface  of  the  glass.  This  process  may  then  be  repeated, 
and  one  cause,  at  least,  of  the  appearance  of  bubbles  in  cells 
of  liquid  will  be  removed.  The  object  to  be  mounted  should 
also  be  soaked  in  one  or  two  changes  of  the  preservative 
liquid  employed,  and,  daring  the  soaking,  be  placed  under 


OF   MICROSCOPIC   OBJECTS.  133 

the  air-pump  and  exhausted.  It  may  then  be  transferred 
to  the  cell,  and  will  probably  cause  the  liquid  to  overflow  a 
little.  The  cover  with  the  gold-size  applied  to  the  edge 
must  then  be  carefully  laid  upon  the  cell,  and  slightly 
pressed  down,  so  that  all  air-bubbles  may  be  displaced.  The 
two  portions  of  gold-size  will  now  be  found  to  adhere 
wherever  the  liquid  does  not  remain,  although  the  whole 
ring  may  have  been  previously  wet.  The  outer  edge  of  the 
thin  glass  and  cell  must  now  be  perfectly  dried,  and  a 
coating  of  gold-size  applied.  When  this  is  dry,  the  process 
must  be  repeated  until  the  cement  has  body  enough  to  pro- 
tect the  cell  from  all  danger  of  leakage.  When  some  pre- 
servative liquids  are  used,  a  scam  is  frequently  found  upon 
the  surface  when  it  is  placed  in  the  cell,  and  this  must 
be  removed  immediately  before  the  cover  is  laid  upon  it. 

I  believe  this  method  to  be  perfectly  secure  against 
leakage  when  carefully  performed ;  and  some  of  my  friends 
have  told  me  that  their  experience  (that  of  some  years)  has 
been  equally  satisfactory. 

In  using  some  of  the  particular  kinds  of  preservative 
liquids,  it  will  be  found  necessary  to  make  a  slight  change 
in  the  manipulation.  This  will  be  best  explained  by  mention- 
ing a  few  objects,  and  the  treatment  they  require. 

For  the  preservation  of  the  Mosses,  Algas,  &c.,  Deane's 
compound  is  much  used,  and  considered  one  of  the  best 
media.  The  specimen  to  be  mounted  should  be  immersed 
in  the  compound,  which  must  be  kept  fluid  by  the  vessel 
containing  it  being  placed  in  hot  water.  In  this  state  the 
whole  should  be  submitted  to  the  action  of  the  air-pump,  as 
it  is  not  an  easy  matter  to  get  rid  of  the  bubbles  which  form 
in  and  around  the  objects.  The  cell  and  slide  must  be 
warmed ;  and  heat  will  also  be  necessary  to  render  the 
gelatine,  &c.,  fluid  enough  to  flow  from  the  stock-bottle. 
The  cell  may  then  be  filled  with  the  compound,  and  the 
specimen  immersed  in  it.  A  thin  glass  cover  must  then  be 
warmed,  or  gently  breathed  upon,  and  gradually  lowered 
upon  the  cell,  taking  care,  as  with  all  liquids,  that  no 


134  PREPARATION  AND   MOUNTING 

bubbles  are  formed  by  the  operation.  The  cover  may  be 
fixed  by  the  aid  of  gold-size,  Japan,  or  any  of  the  usual 
varnishes,  care  being  taken,  as  before,  that  all  the  compound 
is  removed  from  the  parts  to  which  the  varnish  is  intended 
to  adhere. 

The  glycerine  jelly  of  Mr.  Lawrance,  before  mentioned, 
requires  almost  a  similar  treatment.  "  The  objects  to  be 
mounted  in  this  medium  should  be  immersed  for  some  time 
in  a  mixture  of  equal  parts  of  glycerine  and  dilute  alcohol 
(six  of  water  to  one  of  alcohol).  The  bottle  of  glycerine  jelly 
must  be  placed  in  a  cup  of  hot  water  until  liquefied,  when  it 
must  be  used  like  Canada  balsam,  except  that  it  requires 
less  heat.  A  ring  of  asphaltum  varnish  round  the  thin  glass 
cover  completes  the  mounting." 

The  Infusoria  (see  Chapter  IY.)  are  sometimes  preserved 
in  liquid ;  but  present  many  difficulties  to  the  student. 
Different  kinds  require  different  treatment,  and  consequently 
it  is  well,  when  practicable,  to  mount  similar  objects  in  two 
or  more  liquids.  Some  are  best  preserved  in  a  strong 
solution  of  chloride  of  calcium,  others  in  Thwaites'  liquid, 
whilst  a  few  keep  their  colour  most  perfectly  when  in 
glycerine  alone.  There  can  be  little  doubt  that  light  is  the 
bleaching  agent  in  most  cases.  Many  of  them,  however, 
are  so  very  transparent  that  they  present  but  faint  objects 
for  ordinary  observation.  For  this  reason,  however,  they  are 
sometimes  dyed  in  solution  of  magenta  or  other  colour,  as 
elsewhere  noticed.  The  Desmidiacea?  require  somewhat 
similar  treatment,  and  may  be  mentioned  here.  The  solution 
of  chloride  of  calcium  has  been  strongly  recommended ;  but 
no  preservative  liquid  seems  to  be  without  some  action  upon 
them.  Both  of  the  above  classes  of  objects  should  be  mounted 
in  shallow  cells,  so  as  to  allow  as  high  a  microscopic  power 
as  possible  to  be  used  with  them. 

ENTOMOSTRACA. — In  every  ditch  or  place  where  vegetable 
matter  exists,  these  little  active,  jerking  pieces  of  life  are 
certain  to  be  found.  They  are  covered  with  a  horny  trans- 
parent shell,  and  are  various  in  form.  Mr.  Tatem  gives  the 


OF  MICROSCOPIC   OBJECTS.  135 

following,  as  the  best  way  of  preserving  them : — When 
caught  transfer  to  filtered  water  in  watch-glasses  for  twenty- 
four  hours,  in  order  that  the  contents  of  the  laden  intestine 
may  be  discharged.  Draw  off  the  water  and  add  a  little 
spirit  of  wine,  which  quickly  destroys  life.  Remove  all  dirt 
by  aid  of  a  camel-hair  pencil,  and  place  in  a  few  drops  of 
the  medium  used  and  water  (half  of  each)  until  saturation 
is  complete,  and  then  put  up  in  the  medium  in  shallow  cells. 
The  medium  advised  is  Mr.  Farrant's,  whieh  will  be  found 
amongst  those  recommended. 

Many  of  the  ZOOPHYTES  which  are  obtained  on  our  sea- 
coasts  are  well  preserved  by  mounting  iu  cells,  in  the  manner 
before  mentioned,  with  Goadby's  fluid,  or  distilled  water 
with  one  of  the  additions  noticed  amongst  the  preservative 
liquids.  For  examination  by  polarized  light,  however,  they 
are  usually  mounted  in  balsam  (see  Chapter  IV.),  whilst 
those  in  cells  present  a  more  natural  appearance  as  to 
position,  &c.,  for  common  study.  The  POLYZOA,  also,  are 
exquisitely  beautiful  objects  for  the  microscope,  but  require 
some  little  care.  They  should  be  kept  in  sea-water  until 
their  tentacula  are  expanded,  and  may  then  be  readily  killed 
by  plunging  in  cold  fresh  water.  Thus  all  their  beauty  will 
be  preserved,  and  they  may  be  then  mounted  in  one  of  the 
preservative  liquids.  Many  operators  speak  well  of  distilled 
water  well  shaken  with  a  few  drops  of  creosote,  as  before 
mentioned. 

As  to  the  use  of  preservative  liquids  with  the  Diatomaceee 
there  are  various  opinions.  Some  experienced  microscopists 
say  that  there  is  little  or  no  satisfaction  in  mounting  them 
in  this  way.  Dr.  Carpenter,  however,  explains  this  differ- 
ence by  his  instructions  as  to  what  method  should  be  used 
when  certain  ends  are  desired.  He  says :  "  If  they  can  be 
obtained  quite  fresh,  and  it  be  desired  that  they  should 
exhibit  as  closely  as  possible  the  appearance  presented  by 
the  living  plants,  they  should  be  put  up  in  distilled  water 
within  cement  cells  ;.butif  they  are  not  thus  mounted  within 
a  short  time  after  they  have  been  gathered,  about  a  sixth 


136  PREPARATION  AND   MOUNTING 

part  of  alcohol  should  be  added  to  the  water.  If  it  be 
desired  to  exhibit  the  stipitate  forms  in  their  natural  para- 
sitism upon  other  aquatic  plants,  the  entire  mass  may  be 
mounted  in  Deane's  gelatine  in  a  deeper  cell;  and  such  a 
preparation  is  a  very  beautiful  object  for  black-ground 
illumination.  If,  on  the  other  hand,  the  minute  structure  of 
the  silicious  envelopes  is  the  feature  to  be  brought  into 
view,  the  fresh  diatoms  must  be  boiled  in  nitric  or  hydro- 
chloric acid  "  (which  process  is  fully  described  in  Chapter 
III.).  It  is  very  convenient  to  have  many  of  these  objects 
mounted  by  two  or  more  of  the  above  methods  ;  and  if  they 
are  to  be  studied,  this  is  indispensable.  Mr.  Hepworth 
once  showed  me  about  one  hundred  slides  which  he  had 
mounted  in  various  ways,  for  no  other  purpose  than  the 
study  of  the  fly's  foot. 

My  friend,  Mr.  Rylanda,  successfully  mounts  the  diatoms 
in  the  state  in  which  he  finds  them,  and  gave  me  the  follow- 
ing method  as  that  which  he  always  employs.  He  says  that 
he  has  had  no  failures,  and  hitherto  has  found  his  specimens 
unchanged.  Take  a  shallow  ring  cell  of  asphalt  or  black 
varnish  (which  must  be  at  least  three  weeks  old),  and  on  the 
cell,  whilst  revolving,  add  a  ring  of  benzole  and  gold-size 
mixed  in  equal  proportions.  In  a  minute  or  two  pure 
distilled  water  is  put  in  the  cell  until  the  surface  is  slightly 
convex.  The  object  having  been  already  floated  on  to  the 
cover  (the  vessel  used  for  this  purpose  being  an  ordinary 
indian-ink  pallet),  is  now  inverted  and  laid  carefully  upon 
the  water  in  the  cell.  By  these  means  the  object  may  be 
laid  down  without  being  removed.  The  superfluous  moisture 
must  not  be  ejected  by  pressure,  but  a  wetted  camel-hair 
pencil,  the  size  made  in  an  ordinary  quill,  being  partially 
dried  by  drawing  through  the  lips,  must  be  used  repeatedly 
to  absorb  it,  which  the  pencil  will  draw  by  capillary 
attraction  as  it  is  very  slowly  turned  round.  When  the 
cover  comes  in  contact  with  the  benzole  and  gold -size  ring, 
there  is  no  longer  any  fear  of  the  object  being  removed,  and 
a  slight  pressure  with  the  end  of  the  cedar  stick  of  the 


OF  MICROSCOPIC   OBJECTS.  137 

pencil  will  render  the  adhesion  complete,  and  cement  the 
cover  closely  and  firmly  to  the  cell.  When  dry,  an  outer 
ring  of  asphalt  makes  the  mounting  neat  and  complete. 

The  Fungi  have  been  before  mentioned ;  but  it  may  be 
here  stated  that  some  few  of  the  minute  forms  are  best  pre- 
served in  a  very  shallow  cell  of  liquid.  For  this  purpose 
creosote- water  may  be  advantageously  used. 

The  antennae  of  insects  have  been  before  noticed  as  being 
very  beautiful  when  mounted  in  balsam.  This  is  readily 
accomplished  when  they  are  large ;  but  those  of  the  most 
minute  insects  are  much  more  difficult  to  deal  with,  and  are 
less  liable  to  injury  when  put  up  in  fluid.  Goadby's  Fluid 
serves  this  purpose  very  well ;  but,  of  course,  the  object 
must  be  thoroughly  steeped  in  the  liquid  before  it  is 
mounted,  for  a  longer  or  shorter  time  according  to  the 
thickness. 

The  eggs  of  insects  afford  some  worthy  objects  for  the 
microscope,  amongst  which  may  be  mentioned  those  of  the 
common  cabbage  butterflies  (small  and  great),  the  meadow- 
brown,  the  puss-moth,  the  tortoiseshell  butterfly,  the  bug, 
the  cow-dung  fly,  &c.  These,  however,  shrivel  up  on  be- 
coming dry,  and  must,  therefore,  be  preserved  in  some  of 
the  fluids  before  mentioned.  To  accomplish  this  no  parti- 
cular directions  are  required ;  but  the  soaking  in  the  liquid 
about  to  be  employed,  &c.,  must  be  attended  to  as  with  other 
objects. 

Glycerine  may  be  advantageously  used  for  the  preserva- 
tion of  various  insects.  These  should  first  be  cleaned  with 
alcohol  to  get  rid  of  all  extraneous  matter,  and  then,  after 
soaking  in  glycerine,  be  mounted  with  it  like  other  objects. 
There  is,  however,  a  difficulty  in  clearing  glycerine  from 
the  edge  of  the  thin  glass  cover;  but  Mr.  Whalley  told  me 
he  met  with  no  annoyance.  After  laying  the  cover  upon  the 
object  with  the  glycerine,  he  took  away  all  the  superfluous 
liquid  with  a  small  piece  of  linen,  cleaning  it  at  last  with  a 
damped  piece  of  the  same.  The  small  quantity  of  water 
which  gets  mingled  with  the  glycerine  does  no  injury,  and 


138  PREPARATION  AND   MOUNTING 

the  edges  can  be  thus  cleaned  perfectly  enough  for  any 
cement  to  adhere.  Mr.  Suffolk,  at  the  Quekett  Club,  said : 
— When  the  cell  was  closed  he  varnished  it  with  a  coating 
of  common  liquid-glue,  and  when  this  was  dry  he  put  it 
nnder  the  tap  and  thoroughly  washed  it,  in  order  to  remove 
any  glycerine  which  might  remain  outside.  After  carefully 
drying  the  slide  with  blotting-paper,  he  gave  it  another 
coating  of  the  liquid-glue,  and  when  dry  repeated  the  wash- 
ing process,  and  after  having  given  it  a  third  coating  of 
liquid-glue  in  the  same  manner,  he  gave  it  a  final  coat  of 
gold-size,  and  he  never  had  any  trouble  with  cells  closed  in 
this  manner.  Mr.  Hislop,  at  the  same  place,  said : — His 
plan  was,  to  make  a  good  seat  for  the  cover  first  by  a  thick 
ring  of  gum  dammar — allow  this  to  become  sticky ;  next 
put  in  the  glycerine,  lay  on  the  cover,  and  then  carefully 
i  wash  off  all  superfluous  glycerine.  When  perfectly  well- 
washed  and  dried  lay  on  two  or  three  coats  of  gum  dammar 
to  finish  it. 

Some  insects,  such  as  May-flies,  &c.,  are,  however,  often 
preserved  by  immersion  in  a  solution  of  one  part  of  chloride 
of  calcium  in  three  or  four  parts  of  water ;  but  this  has  not 
been  recommended  amongst  the  preservative  liquids,  as  the 
colour,  which  is  often  an  attractive  quality  of  this  class  of 
objects,  is  thereby  destroyed. 

We  have  now  noticed  the  treatment  which  must  be  ap- 
plied to  those  objects  which  are  to  be  preserved  in  liquids 
and  cells.  We  may  here  state  that  all  slides  of  this  kind 
should  be  examined  at  short  intervals,  as  they  will  be  found 
now  and  then  to  require  another  coating  of  varnish  round 
the  edge  of  the  thin  glass  cover  to  prevent  all  danger  of 
leakage.  The  use  of  the  air-pump,  in  the  first  instance 
(as  before  recommended),  and  this  precaution  as  to  the 
varnish,  will  render  the  slides  less  liable  to  leakage  and  air- 
bubbles,  which  so  very  frequently  render  them  almost 
worthless. 


OF   MICROSCOPIC   OBJECTS.  139 


CHAPTER   VI. 

SECTIONS  AND   HOW   TO   CUT   THEM,   WITH   SOME   REMARKS   ON 
DISSECTION.* 

MANY  objects  are  almost  worthless  to  the  microscopist  until 
extraneous  matter  is  removed  from  them ;  and  this  is  fre- 
quently difficult  in  the  extreme  to  perform  satisfactorily.  As 
an  instance,  certain  Foraminifera  may  be  mentioned  in  which 
the  cells  are  placed  one  upon  another,  consequently  the  ob- 
ject must  be  reduced  to  a  certain  degree  of  thinness  before  a 
single  uniform  layer  of  these  cells  can  be  obtained  to  show 
something  of  the  internal  arrangements. 

Most  animal  and  vegetable  forms  require  an  examination 
of  the  separate  parts  before  much  can  be  known  about  them. 
The  mass  must  be  divided  into  separate  portions,  each  part 
intended  to  be  preserved  being  cleaned  from  the  useless 
matter  with  which  it  is  surrounded.  It  will  frequently  be 
found  necessary  to  make  thin  sections,  which  from  a  very 
tender  substance  is  no  easy  matter ;  and  much  patience  will 
be  necessary  to  attain  anything  like  proficiency. 

This  making  of  sections  was  not  until  very  recently 
undertaken  by  many  except  those  belonging  to  the  medical 
profession,  but  I  do  not  see  why  this  should  be  so,  as  much 
may  be  accomplished  by  a  persevering  and  interested  mind 
where  there  is  time  for  entering  into  the  subject.  I  will 
therefore  make  an  attempt  to  give  some  instructions  on  this 
subject  also.  We  will  first  consider  the  cutting  of  sections 
from  hard  substances,  in  which  the  ordinary  knife,  chisel, 

*  As  some  knowledge  of  dissection  is  necessaiy  to  success  in  injec- 
tion, additional  matter  on  this  subject  will  be  found  in  Chapter  VII. 


140  PREPARATION   AND   MOUNTING 

&c.,  are  of  no  avail.  Most  of  these  require  no  particular 
care  in  mounting,  but  are  placed  in  balsam  like  the  other 
objects  noticed  in  Chapter  IV.:  where,  however,  any  special 
treatment  is  necessary  it  will  be  commented  upon  as  we 
proceed. 

SHELLS,  &c. — It  is  seldom,  if  ever,  necessary  to  possess 
apparatus  for  this  process  except  a  small  thin  saw  made 
with  a  steel  blade,  for  which  a  piece  of  watch-spring  serves 
very  well ;  a  fine  stone  such  as  is  used  for  sharpening  pen- 
knives ;  and  two  smooth  leather  strops,  one  of  which  is  to 
be  used  with  putty-powder  to  polish  the  section  after  grind- 
ing, and  the  other  dry,  to  give  the  final  surface.  It  is,  how- 
ever, very  convenient  to  have  three  or  four  files  of  different 
degrees  of  fineness.  A  very  useful  implement  in  this  process 
is  the  Corundum  file  or  rubber,  sold  by  most  dealers  in 
watchmakers'  tools.  It  may  be  procured  of  almost  any  size 
or  grain,  either  circular  or  flat,  and  will  cut  almost  any- 
thing. They  possess  the  very  great  advantage  of  not  carry- 
ing much,  if  any,  impurity  into  the  texture  of  the  object 
upon  which  they  are  used.  The  shell,  if  very  thick,  may  be 
divided  by  using  the  watch-spring  saw ;  and  this  section 
may  then  with  ordinary  care  be  rubbed  down  with  water  on 
the  stone  until  one  side  of  it  is  perfectly  flat.  When  this  is 
accomplished  it  must  be  rubbed  with  putty-powder  upon 
the  strop,  and  finally  upon  the  other  strop  without  the 
powder.  This  surface  will  then  be  finished,  and  must  be 
firmly  united  to  the  slide  in  the  position  it  is  intended  to 
occupy.  To  do  this  a  small  quantity  of  Canada  balsam  may 
be  dropped  upon  the  middle  of  the  slide  and  heated  over 
the  lamp  until  on  cooling  it  becomes  hard ;  but  this  must 
be  stopped  before  it  is  rendered  brittle.  Upon  this  the 
polished  surface  must  be  laid,  and  sufficient  heat  applied  to 
allow  the  object  to  fall  closely  upon  the  slide,  when  slight 
pressure  may  be  used  to  force  aside  all  bubbles,  &c.  On 
cooling,  the  adherence  will  be  complete  enough  to  allow  the 
same  grinding  and  polishing  upon  the  upper  surface  which 
the  lower  received.  Whilst  undergoing  this,  the  section 


OF  MICROSCOPIC  OBJECTS.  141 

must  be  examined  from  time  to  time  to  ascertain  whether 
the  necessary  degree  of  thinness  has  been  reached.  When 
this  is  the  case  the  section  should  be  washed  thoroughly  and 
dried.  It  must  then  be  covered,  which  is  best  done  by  using 
ordinary  Canada  balsam,  as  recommended  in  Chapter  IY. ; 
or,  if  the  section  is  to  be  mounted  dry,  it  must  be  freed  from 
balsam  by  washing,  or  soaking  if  necessary,  in  turpentine 
or  other  solvents. 

Sections  of  some  exquisitely  beautiful  objects  are  cut  with 
much  less  trouble  than  the  above.  The  Orbitolite,  for 
instance,  may  be  prepared  in  this  manner.  Take  the  object 
and  by  pressure  with  the  finger  rub  the  side  upon  a  flat  and 
smooth  sharpening  stone  with  water  until  the  portion  is 
reached  which  it  is  wished  to  show.  The  strength  of  the 
object  will  easily  allow  this  to  be  accomplished  with  ordinary 
care.  This  side  may  then  be  attached  to  the  glass  slide 
with  heated  balsam,  as  above  described,  and  the  object  may 
then  be  gently  rubbed  down  to  the  degree  of  thinness  re- 
quired to  show  it  to  the  best  advantage.  After  removing 
all  disengaged  matter  from  the  object  by  washing  and 
thoroughly  drying,  it  may  be  mounted  in  balsam  in  the 
usual  manner,  when  it  is  equally  beautiful  as  a  transparent 
or  opaque  object.  From  this  it  will  be  seen  that  in  many 
instances  where  a  smooth  stone  is  found  sufficient  for  the 
work  (which  is  often  the  case  when  the  section  is  mounted 
in  balsam)  the  final  process  of  polishing  advised  above  may 
be  dispensed  with,  as  in  the  Orbitolite,  Nummulite,  &c.,  &c. 
It  is  quite  necessary  that  the  stones  on  which  the  objects 
are  rubbed  be  perfectly  flat,  otherwise  one  side  must  be 
acted  upon  before  the  other,  and  it  will  be  found  impos- 
sible to  attain  anything  like  uniformity.  Where  it  is  not 
practicable  to  cut  a  section,  and  the  object  is  very  thick,  a 
coarse  stone  may  be  first  used  to  reduce  it  and  the  smoother 
afterwards. 

The  consideration  of  the  cutting  of  sections  from  shells 
would  scarcely  be  deemed  complete  without  some  mention  of 
what  Dr.  Carpenter  terms  the  decalcifying  process.  Muriatic 


142  PREPARATION   AND   MOUNTING 

acid  is  diluted  with  twenty  times  its  volume  of  water,  and 
in  this  the  shell  is  immersed.  After  a  period,  differing  ac- 
cording to  the  thickness  of  the  shell,  the  carbonate  of  lime 
will  be  dissolved  away,  and  a  peculiar  membrane  left,  show- 
ing the  structure  of  the  shell  very  perfectly.  This  may  be 
mounted  dry,  in  balsam,  or  sometimes  in  liquid,  according 
to  the  appearance  of  the  object;  but  no  rule  can  be  given. 
The  discretion  of  the  student,  however,  will  enable  him  to 
choose  the  most  suitable  method. 

From  some  shells  it  is  easy  to  divide  thin  plates,  or 
laminae,  which  require  nothing  but  mounting  in  Canada 
balsam  to  show  the  texture  very  well.  In  working,  however, 
with  those  which  are  pearly,  it  will  be  found  that  expe- 
rience and  patience  are  needed,  as  they  are  very  brittle  and 
peculiarly  hard ;  but  a  little  practice  will  overcome  these 
difficulties. 

Amongst  the  Echinodermata,  which  include  the  star- 
fishes, sea-hedgehogs,  &c.,  there  are  many  whose  outer  sur- 
face is  covered  with  spines,  or  thin  projections.  Some 
of  these  are  sharp  and  thorn-like,  others  blunt,  longer  or 
shorter,  and,  indeed,  of  endless  variety.  In  many  of  these, 
when  a  section  is  made,  rings  are  seen  which  have  a  common 
centre,  with  radiating  supports,  resembling  sections  of  some 
of  the  woods.  These  are  very  beautiful  objects,  and  methods 
of  procuring  them  may  now  be  considered.  It  is  the  best 
to  cut  as  thin  a  section  as  can  safely  be  got  with  the  watch- 
spring  saw  first,  when  the  smooth  sharpening  stone  may 
be  used  to  polish  one  side,  which  is  easily  accomplished  with 
water  only.  When  this  is  effected,  it  must  be  washed  clean, 
and  thoroughly  dried,  and  then  may  be  united  to  the  slide 
in  the  same  manner  as  before  recommended  for  the  Orbito- 
lite,  &c.  If  it  is  ever  necessary  to  displace  it  on  account 
of  inequalities,  bubbles,  or  other  remediable  fault,  this  may 
be  done  by  warming  the  slide;  though  too  much  heat  must 
be  avoided,  otherwise  fresh  bubbles  will  certainly  be  pro- 
duced. The  covering  with  thin  glass,  balsam,  &c.,  will 
present  no  difficulty  to  the  student ;  but  he  must  remember 


or  MICKOSCOPIC  OBJECTS.  143 

that  the  transparency  is  somewhat  increased  by  this  last 
operation. 

Corals  are  often  treated  in  this  way,  in  order  to  reveal 
their  structure.  Except,  however,  the  student  has  had 
much  practice,  he  will  often  find  this  a  most  difficult  task, 
as  many  of  them  are  exceedingly  brittle  and  hard.  He  will 
find  the  method  before  described  equally  applicable  here, 
and  should  take  both  horizontal  and  vertical  sections. 

COAL. — This  substance  is  one  of  the  most  interesting 
objects  to  the  microscopist.  It  is,  of  course,  of  vegetable 
origin ;  and  though  it  is  in  many  cases  in  such  minute 
separate  portions  as  to  have  lost  all  appearance  of  vegeta- 
tion, yet  it  is  very  frequently  met  with  in  masses,  bearing 
the  form,  even  to  the  minute  markings,  of  wood,  in  various 
directions.  To  see  this  and  prepare  it  for  microscopic  re- 
search, a  suitable  piece  of  coal  must  be  obtained ;  but  in 
every  case  the  cutting  and  preparation  of  these  sections 
require  great  care  and  skill.  Sometimes  the  coal  is  first 
made  smooth  on  one  side,  fastened  to  the  glass,  reduced  to 
the  requisite  degree  of  thinness,  and  finished  in  the  method 
before  described.  This  mode  of  treating  it  is  sometimes, 
however,  very  tantalizing,  as,  at  the  last  moment,  when  the 
section  is  about  thin  enough,  it  often  breaks  up,  and  so 
renders  the  trouble  bestowed  upon  it  fruitless.  The  dark 
colour  and  opacity  of  coal  render  an  extraordinary  thinness 
necessary,  and  so  increase  the  liability  to  this  accident. 

Mr.  Slade  recommends  that  the  piece  of  coal,  having  been 
smoothed  on  one  side,  be  cemented  on  that  side  to  a  glass 
slip  by  marine-glue  of  the  best  quality,  quite  free  from 
undiasolved  or  foreign  matter.  Great  care  must  be  taken 
to  press  out  all  air-bubbles,  the  coal  breaking  up  at  such 
places  as  it  gets  thin,  a  hole  resulting.  It  may  then  be 
reduced  in  the  usual  way,  and  when  thin  enough  mounted 
in  Canada  balsam  and  covered  by  thin  glass. 

Perhaps  the  best  method  which  can  be  pursued  is  that 
recommended  in  the  Micrographic  Dictionary,  which  is 
as  follows  : — "  The  coal  is  macerated  for  about  a  week  in  a 


144  PREPARATION   AND   MOUNTING 

solution  of  carbonate  of  potash ;  at  the  end  of  that  time  it 
is  possible  to  cat  tolerably  thin  slices  with  a  razor.  Thet:e 
slices  are  then  placed  in  a  watch-glass  with  strong  nitric 
acid,  covered,  and  gently  heated ;  they  soon  turn  brownish, 
then  yellow,  when  the  process  must  be  arrested  by  dropping 
the  whole  into  a  saucer  of  cold  water,  else  the  coal  would 
be  dissolved.  The  slices  thus  treated  appear  of  a  darkish 
amber  colour,  very  transparent,  and  exhibit  the  structure, 
when  existing,  most  clearly.  We  have  obtained  longitudinal 
and  transverse  sections  of  coniferous  wood  from  various 
coals  in  this  way.  The  specimens  are  best  preserved  in 
glycerine  in  cells;  we  find  that  spirit  renders  them  opaque, 
and  even  Canada  balsam  has  the  same  defect.  Schultze 
states  that  he  has  brought  out  the  cellulose  reaction  with 
iodine  in  coal  treated  with  nitric  acid  and  chlorate  of 
potash."  Now  and  then  in  coal  we  meet  with  a  half- 
formed  carbon-looking  substance  which  is  no  more  difficult 
to  work  with  than  ordinary  charcoal.  From  this  it  is  an 
easy  thing  to  procure  interesting  slides. 

Cannel-coal  is  so  close  and  firm  in  its  structure  as  to  be 
much  used  instead  of  jet  in  the  manufacture  of  ornaments  : 
it  takes  a  beautiful  polish,  and  consequently  presents  the 
student  with  none  but  ordinary  difficulties  in  getting 
sections  of  it.  Its  formation  is  somewhat  different  from 
that  of  coal,  sometimes  showing  the  transition  very  clearly. 

Fossil  Wood. — This  is  very  often  brittle  and  requires 
great  care  in  cutting.  There  are,  however,  different  kinds 
of  fossil  wood,  but  to  obtain  anything  like  certainty  and 
perform  much  work  a  lathe  is  necessary.  I  know  of  no 
method  better  than  that  given  by  Mr.  Butterworth,  and 
shall  therefore  make  use  of  his  words.  First,  I  will  begin 
with  the  cutting.  To  the  framework  of  an  ordinary  foot- 
lathe  I  attach  an  upright  spindle  (see  engraving).  On  this 
upright  spindle  I  drive  by  a  band  passing  over  "carry- 
pulleys  "  from  the  wheel  below.  On  the  top  of  this  spindle 
I  fix  my  cutting-disc,  which  is  made  from  a  very  thin 
piece  of  sheet  iron,  and  is  about  six  inches  in  diameter. 


OF   MICROSCOPIC   OBJECTS. 


145 


The  edge  of  this  saw  I  charge  with  diamond-powder.  To 
the  edge  of  the  saw  I  hold  my  specimen,  and  as  it  cuts  I 
lubricate  the  edge  with  a  small  brush  dipped  in  turpentine. 


With  this  method  I  have  cut  sections  of  fossil  wood  so  thin 
that  all  its  structure  has  been  well  defined  and  required 
nothing  but  mounting  in  balsam ;  this  has  been  silicated 
fossil  wood.  In  cutting  calcareous  fossil  wood,  I  have  to 
cut  the  sections  thicker  and  grind  them  down.  My  grinding 
apparatus  is  composed  of  leaden  laps,  which  I  make  to 
revolve  in  a  horizontal  position  on  the  same  upright  spindle 


146  PREPAKATION   AND   MOUNTING 

on  which  I  fix  my  cutting  saw.  I  use  two  laps,  one  for 
rough  grinding,  the  other  for  smoothing.  I  use  ]STo.  1. 
emery  and  a  little  water  with  the  first,  and  flour  of  emery 
with  plenty  of  water  on  the  second.  In  preparing  a  speci- 
men, I  first  grind  a  smooth  surface  on  one  side,  and  then 
fix  it  to  a  plate  of  glass,  of  such  a  size  as  will  suit  my 
specimen,  with  Canada  balsam.  I  then  reduce  it  in  thickness 
on  the  rough  lap  till  I  begin  to  see  the  light  through  it. 
Then  I  begin  with  the  smoothing  lap,  and  reduce  it  with 
flour  of  emery  until  every  part  of  its  structure  is  distinct. 
If  I  choose  to  polish  the  specimen  I  do  so  on  a  lap  made 
of  plush  cloth  or  cotton  vevet  and  putty-powder.  I  then 
float  them  off  the  slide  on  which  they  have  been  ground, 
and  fix  them  on  another  with  Canada  balsam.  I  prefer, 
where  it  is  practicable,  to  mount  them  in  balsam  under  a 
thin  cover  in  the  usual  way,  as  I  am  satisfied  that  the 
structure  is  better  brought  out. 

In  flint  there  are  often  found  remains  of  sponges,  shell?, 
Diatomaceae,  &c. ;  but  to  show  these  well,  sections  must  be 
cut  and  polished  by  the  lathe  and  wheel  of  the  lapidary, 
which  the  microscopic  student  seldom  possesses.  Thin  chip- 
pings  may,  however,  be  made,  which  when  steeped  in  turpen- 
tine and  mounted  in  balsam,  will  frequently  show  these 
remains  very  well. 

Teeth -are  very  interesting  objects  to  all  microscopists, 
more  especially  to  those  who  give  much  study  to  them ;  as 
the  class  of  animal  may  very  frequently  be  known  from  one 
solitary  remaining  tooth.  To  examine  them  thoroughly,  it 
is  necessary  to  cut  sections  of  them  ;  but  this  is  rather  diffi- 
cult to  perform  well,  and  needs  some  experience.  Some 
instructions,  however,  will  at  least  lessen  these  difficulties, 
and  we  will  now  endeavour  to  give  them. 

Sections  of  teeth  and  bone  may  be  successfully  made  by 
rubbing  slices  cut  with  a  saw  between  two  plates  of  ground 
glass,  with  water  and  a  little  powdered  pumice-stone,  the 
old  and  partially  worn  glass  being  kept  for  the  final 
polishing  of  the  sections. 


OP   MICROSCOPIC   OBJECTS.  147 

Tt  is  generally  thought  that  Canada  balsam  injures  the 
finer  markings  of  these  sections,  consequently,  they  are 
almost  invariably  mounted  dry.  A  thin  piece  is  first  cut 
from  the  tooth  with  the  saw  of  watch-spring  before 
mentioned,  if  possible;  but.  should  the  substance  be  too 
hard  for  this,  the  wheel  and  lathe  must  be  used  with 
diamond  dust.  If  this  cannot  be  procured,  there  is  no 
alternative  but  to  rub  down  the  whole  substance  as  thin  as 
practicable  on  some  coarse  stone  or  file,  or  best  of  all  the 
corundum  rubber.  The  surface  will  then  be  rough ;  but 
this  may  be  much  reduced  by  rubbing  upon  a  flat  sharp- 
ening stone  with  the  finger,  or  a  small  piece  of  gutta-percha 
upon  the  object  to  keep  it  in  contact.  The  scratches  may 
be  much  lessened  by  this,  but  not  so  thoroughly  removed  as 
microscopic  examination  requires  in  dry  sections.  It  must, 
therefore,  be  polished  with  the  putty-powder  and  dry  strop, 
as  recommended  in  the  working  of  shell-sections.  The 
other  side  of  the  section  of  the  tooth  may  then  be  rubbed 
down  to  the  requisite  thinness,  and  polished  in  the  same 
manner,  when  the  dust  and  other  impurities  must  be  re- 
moved by  washing,  after  which  the  section  must  be  carefully 
dried  and  mounted.  Sometimes  it  may  be  deemed  desirable 
to  make  a  preparation  of  the  teeth  in  situ;  for  this  purpose 
take  the  lower  jaw  of  some  animal  like  the  rat,  weasel,  or 
guinea-pig,  and  soak  it  in  absolute  alcohol  first,  let  that  evapo- 
rate out,  then  soak  in  the  solution  of  balsam  and  benzole  ; 
when  that  has  evaporated  to  hardness,  grind  down  the  jaw  as 
a  section,  the  teeth  are  fixed  in  by  the  balsam.  Some  of 
these  sections  are  equally  interesting  as  opaque  or  trans- 
parent objects. 

The  dentine  of  the  teeth  may  be  decalcified  by  immersion 
of  the  section  in  dilute  muriatic  acid;  after  drying  and  mount- 
ing in  Canada  balsam  it  presents  a  new  and  interesting 
appearance,  showing  the  enamel  fibres  very  beautifully 
when  magnified  about  three  hundred  diameters.  A  friend 
tells  me  that  after  submersion  of  the  ivJiole  tooth  in  the  acid 
he  has  been  able  to  cut  sections  with  a  razor. 

L2 


148  PREPARATION  "AND   MOUNTING 

SECTIONS  or  BONE. — With  the  aid  of  the  microscope  few 
fragmentary  remains  have  proved  so  useful  to  the  geologist 
and  students  of  the  fossil  kingdom  as  these.  From  a  single 
specimen  many  of  our  naturalists  can  tell  with  certainty  to 
what  class  of  animal  it  has  once  belonged.  To  arrive  at 
this  point  of  knowledge  much  study  is  necessary,  and  sections 
of  various  kinds  should  be  cut  in  such  a  manner  as  will  best 
exhibit  the  peculiarities  of  formation.  The  methods  of 
accomplishing  this  will  now  be  considered.  It  may,  how- 
ever, be  first  mentioned  that  the  chippings  of  some  bones 
will  be  found  useful  now  and  then,  as  before  stated  with 
flint,  though  this  is  by  no  means  a  satisfactory  way  of  pro- 
ceeding. Sometimes  the  bones  may  be  procured  naturally  so 
thin  that  they  maybe  examined  without  any  cutting;  and  only 
require  mounting  dry,  or  in  fluid,  as  may  be  found  the  best. 

When  commencing  operations  we  must  provide  the  same 
apparatus  as  is  needed  in  cutting  sections  of  teeth,  before 
described.  A  fine  saw,  like  those  used  for  cutting  brass, 
&c.,  two  or  three  flat  files  of  different  degrees  of  coarseness  ; 
two  flat  "  sharpening "  stones ;  and  a  leather  strop  with 
putty-powder  for  polishing.  As  thin  a  section  as  possible 
should  first  be  cut  from  the  part  required  by  the  aid  of  the 
fine  saw ;  and  it  is  better  when  in  this  state  to  soak  it  for 
some  short  time  in  camphine,  ether,  or  some  other  spirit  to 
free  it  from  all  grease.  With  the  aid  of  a  file  we  may  now 
reduce  it  almost  to  the  necessary  degree  of  thinness,  and 
proceed  as  before  recommended  with  teeth.  The  "  sharpen- 
ing "  stone  will  remove  all  scratches  and  marks  sufficiently 
to  allow  it  to  be  examined  with  the  microscope  to  see  if  it  is 
ground  thin  enough  ;  and  if  it  is  to  be  mounted  dry  we  must 
polish  it  with  putty-powder  and  water  upon  the  strop  to  as 
high  a  degree  as  possible,  and  having  washed  all  remains  of 
polishing  powder,  &c.,  from  the  section  we  must  place  it 
upon  the  slide  and  finish  it  as  described  in  Chapter  III. 
But  where  these  sections  are  required  for  mounting  in 
balsam  a  less  amount  of  polish  is  necessary  ;  thus  rendering 
the  whole  process  much  more  readily  completed. 


OF   MICROSCOPIC   OBJECTS.  149 

If  the  bone  is  not  sufficiently  hard  in  its  nature  to  bear 
the  above  method  of  handling  whilst  grinding  and  polishing 
— as  some  are  far  more  brittle  than  others — as  thin  a  section 
as  possible  must  first  be  cut  with  the  saw,  and  one  surface 
ground  and  polished.  The  piece  must  then  be  dried  and 
united  to  the  glass  by  heated  balsam  in  the  same  manner 
as  shells,  &c.  After  which  the  superabundance  of  balsam 
must  be  removed  from  the  glass ;  then  rub  down  upon  the  stone 
and  strop  as  before.  Great  care  must  be  taken  that  the  canals 
be  not  filled  during  the  process  with  the  dust  of  the  bone, 
or  of  the  polishing  material.  Dr.  Beale,  in  the  journal  of 
the  Q.  M.  C.  takes  occasion  to  say  "  that  he  cannot  admit 
that  the  best  way  of  preparing  such  sections  is  by  grinding 
down,  since  it  is  too  liable  to  fill  the  canals  with  debris."  He 
recommends  that  a  fresh  bone  be  taken — and  a  small  slice 
cut  off  by  a  strong  sharp  knife.  This  is  then  to  be  im- 
mersed in  carmine  dissolved  in  ammonia — the  ammonia 
being  first  neutralized  by  acetic  acid.  The  walls  of  the 
vessels  which  penetrate  the  lacunae  and  canaliculi  are  by 
this  means  stained  crimson,  and  thus  the  true  structure  of 
bone  is  rendered  visible.  When  the  polishing  is  completed 
the  whole  slide  must  be  immersed  in  chloroform,  ether,  or 
some  other  spirit,  to  release  and  cleanse  the  section,  when 
it  may  be  mounted  as  the  one  above  mentioned. 

Some  have  recommended  a  strong  solution  of  isinglass  to 
affix  the  half-ground  teeth  or  bones  to  the  glass  as  causing 
them  to  adhere  very  firmly  and  requiring  no  heat,  and  also 
being  readily  detached  when  finished. 

The  reason  why  the  sections  of  bone  are  usually  mounted 
dry  is  that  the  lacunce,  bone  cells,  and  canaliculi  (re- 
sembling minute  canals)  show  their  forms,  &c.,  very  per- 
fectly in  this  state,  as  they  are  hollow  and  contain  air, 
whereas  if  they  become  filled  with  liquid  or  balsam — which 
does  sometimes  occur — they  become  almost  indistinguishable. 
There  are  some  dark  specimens,  however,  where  the  cells  are 
a'ready  filled  with  other  matter,  and  it  is  well  to  mount  these 
•with  balsam  and  so  gain  a  greater  degree  of  transparency. 


150  PREPARATION  AND  MOUNTING 

To  obtain  a  true  knowledge  of  the  structure  of  bone, 
sections  must  be  cut  as  in  wood,  both  transversely  and 
longitudinally;  but  with,  fossil  bones,  without  the  lapidary's 
wheel,  it  is  a  laborious  task,  and  indeed  can  seldom  be 
properly  accomplished.  In  this  place,  also,  it  may  be 
mentioned  that  by  submitting  bone  to  the  action  of  muriatic 
acid  diluted  ten  or  fifteen  times  with  water,  the  lime,  &c.,  is 
dissolved  away  and  the  cartilage  is  left,  which  may  be  cut 
into  sections :  in  caustic  potash  the  animal  matter  is  got 
rid  of.  Both  of  these  preparations  may  be  mounted  in 
fluid. 

The  method  of  cutting  thin  sections  of  bone  may  be  also 
employed  with  the  stones  of  fruit,  vegetable  ivory,  and  such 
like  substances ;  many  of  which  show  a  most  interesting 
arrangement  of  cells,  especially  when  the  sections  are  trans- 
verse. Most  of  these  objects  present  a  different  appearance 
when  mounted  dry  to  that  which  they  bear  when  in  balsam, 
owing  to  the  cells  becoming  filled ;  and  to  arrive  at  a  true 
knowledge  of  them  we  must  have  a  specimen  mounted  in 
both  ways. 

Some  will  perhaps  remark  that  most  of  the  directions  for 
section  cutting  are  given  to  those  who  are  totally  without 
artificial  power,  and  must  rely  upon  their  own  manual  exer- 
tions. I  reply  that  these  hints  are  mostly  given  to  such  ; 
but  Mr.  Butterworth's  directions  to  use  the  lathe  are  so 
ample,  that  a  repetition  of  them  at  the  mention  of  each  class 
of  "  sectional "  substance  would  be  mere  tautology. 

To  those  who  study  polarized  light,  few  objects  are  more 
beautiful  than  sections  of  the  different  kinds  of  horn.  We 
will  briefly  inquire  into  the  best  method  of  cutting  these. 
There  are  three  kinds  of  horn,  the  first  of  which  is  hard, 
as  the  stag's,  and  must  be  cut  in  the  same  manner  as  bone. 
The  second  is  somewhat  softer,  as  the  cow's.  The  third  is 
another  and  still  softer  formation,  aa  the  "  horn  "  (as  it  is 
termed)  of  the  rhinoceros.  In  cutting  sections  of  the  two 
last  we  should  succeed  best  by  using  the  machine  invented 
for  these  purposes,  which  I  shall  shortly  describe  when  the 


OF  MICROSCOPIC   OBJECTS.  151 

method  of  cutting  wood  is  considered.  To  aid  us  in  this 
when  the  horn  is  hard  it  must  be  boiled  for  a  short  time  in 
water,  after  which  the- cutting  will  be  more  easily  affected. 
The  sections  should  be  both  transverse  and  longitudinal, 
those  of  the  former  often  showing  cells  with  beautiful  crosses, 
the  colours  with  the  selenite  plate  being  truly  splendid.  Of 
this  class  the  rhinoceros  horn  is  one  of  the  best ;  but  the 
buffalo  also  affords  a  very  handsome  object.  The  cow's,  and 
indeed  almost  every  different  kind  of  horn,  well  deserves  the 
trouble  of  mounting.  Whalebone,  when  cut  transversely, 
strongly  resembles  those  of  the  third  and  softer  formation. 
All  these  are  best  seen  when  mounted  in  Canada  balsam, 
but  care  must  be  taken  that  they  have  been  thoroughly  dried 
after  cutting,  and  then  steeped  in  turpentine. 

An  interesting  object  may  also  be  procured  from  whale- 
bone by  cutting  long  sections  of  the  hairs  of  which  it  is 
composed.  Down  the  centre  of  each  hair  we  shall  find  a 
line  of  cells  divided  from  one  another  very  distinctly.  And 
(as  recommended  in  the  Micrographic  Dictionary)  if 
whalebone  be  macerated  twenty-four  hours  in  a  solution  of 
caustic  potash  it  will  be  softened,  and  by  afterwards  digest- 
ing in  water,  the  outer  part  will  be  resolved  into  numerous 
transparent  cells,  which  will  show  more  plainly  the  structure 
of  this  curious  substance. 

An  object  which  frequently  comes  to  the  hand  of  any 
man  who  moves  about  in  the  world  is  a  porcupine  quill. 
This  is  a  really  valuable  object  for  the  microscopist.  Trans- 
verse and  longitudinal  sections  possess  their  respective 
beauty;  and  their  appearance  varies  somewhat  as  to  the 
distance-  from  the  point  at  which  the  section  is  made. 
Soaking  in  hot  water  for  a  short  time  renders  it  easy  enough 
to  cut,  and  when  dry  and  mounted  in  balsam  the  student  is 
well  repaid. 

In  a  former  chapter,  hairs  were  mentioned,  their  many 
and  interesting  forms,  and  their  beauty  when  used  with 
polarized  light.  The  sections  of  them,  however,  are  no  less 
a  matter  of  study,  as  this  mode  of  treatment  opens  to  sight 


152  PREPARATION  AND   MOUNTING 

the  outer  "  casing,"  and  the  inner  substance  somewhat  re- 
sembling the  pith  of  plants. 

It  would  be  out  of  place  to  enter  into  the  description 
of  the  different  forms  met  with ;  but  the  ways  in  which 
sections  are  to  be  procured  may  be  noticed.  If  transverse 
sections  are  required,  some  place  a  quantity  of  hairs  betwixt 
two  flat  pieces  of  cork,  which  by  pressure  hold  them  firmly- 
enough  together  to  allow  the  required  portions  to  be  cut 
with  a  razor.  Others  take  a  bundle  of  the  hairs  and  dip 
it  into  gum  or  glue,  which  gives  it  when  dry  a  solidity  equal 
to  wood.  Sections  of  this  are  then  cut  with  the  machine 
mentioned  a  little  further  on,  and  these  may  be  mounted  in 
balsam.  The  human  hair  is  easily  procured  in  the  desired 
sections  by  shaving  as  closely  as  possible  a  second  time  and 
cleansing  from  the  lather,  &c.,  by  carefully  washing.  Most 
hairs,  however,  should  be  examined  both  transversely  and 
longitudinally.  It  is  not  difficult  to  procure  the  latter,  as 
we  may  generally  split  them  with  the  aid  of  a  sharp  razor. 
In  a  great  number  of  hairs  there  is  a  quantity  of  greasy 
matter  which  must  be  removed  by  soaking  in  ether  or  some 
other  solvent  before  mounting. 

We  may  next  consider  the  best  method  of  procuring 
sections  of  wood,  which  must  be  cut  of  such  a  degree  of 
thinness  as  to  form  transparent  objects,  and  so  display  all 
the  secrets  of  their  structure.  There  is  no  monotony  in 
this  study,  as  the  forms  are  so  various,  and  the  arrange- 
ment of  the  cells  and  woody  fibre  so  different,  that  the 
microscopist  may  find  endless  amusement  or  study  in  it. 
From  a  single  section  the  class  of  trees  to  which  it  has 
belonged  may  be  known,  often  even  when  the  wood  is  fossil. 
The  apparatus  best  adapted  for  cutting  these  sections  is 
made  as  follows  : — A  flat  piece  of  hard  wood,  about  six 
inches  long,  four  wide,  and  one  thick,  is  chosen,  to  which 
another  of  the  same  size  is  firmly  fixed,  so  as  to  form,  in 
a  side  view,  the  letter  J.  On  one  end  of  the  npper  surface 
is  fastened  a  brass  plate,  perfectly  flat,  in  the  centre  of  which 
a  circular  opening  is  cut  about  half  an  inch  in  diameter. 


OP   MICROSCOPIC   OBJECTS.  153 

Coinciding  with  this  opening  is  a  brass  tube,  fixed  in  the 
tinder  side  of  the  table  (if  it  may  be  termed  so).  This  tube 
is  so  cut  at  the  bottom  as  to  take  a  fine  screw.  Another 
screw  is  also  placed  at  the  same  end  of  the  "  table,"  which 
works  at  right  angles  to  this,  so  that  any  substance  in  the 
tube  may  be  wedged  firmly  by  working  this  last  screw.  To 
use  this  instrument,  the  piece  of  wood  or  other  object  of 
which  a  section  is  required  must  be  placed  in  the  tube, 
when,  by  turning  the  screw  underneath,  the  wood  is  raised 
above  the  brass  plate  more  or  less  as  wished,  and  by  using 
the  screw  at  the  end,  it  is  held  firmly  in  the  same  position. 
With  a  flat  chisel  the  portion  of  the  object  which  projects 
above  the  surface  of  the  brass  plate  may  now  be  cut  off,  and 
by  means  of  the  bottom  screw  another  portion  may  be 
raised  and  treated  in  the  same  manner.  As  to  the  thickness 
of  which  objects  should  be  cut,  no  proper  directions  can  be 
given,  as  this  differs  so  greatly  that  nothing  but  experience 
can  be  any  guide.  The  same  thickness  can  be  obtained  by 
working  the  screw  underneath  in  uniform  degrees,  the  head 
being  marked  for  this  purpose  ;  and  where  the  substance  to 
be  cut  is  very  much  smaller  than  the  hole  in  the  brass  plate, 
it  may  be  wedged  with  cork. 

*As  this  instrument  is  peculiarly  adapted  for  cutting 
wood  (though  used  for  other  substances,  as  before  men- 
tioned), I  shall  notice  a  few  particulars  concerning  this 
branch  of  sections.  It  may  here  be  remarked,  that  to 
obtain  anything  like  a  true  knowledge  of  the  nature  of 
wood,  it  should  be  cut  and  examined  in  at  least  two  direc- 
tions, across  and  along.  The  piece  of  wood  is  often  placed 
in  spirits  for  a  day  or  two,  so  that  all  resinous  matter  may 
be  dissolved  out  of  it ;  it  must  then  be  soaked  in  water  for 

*  M.  Mouchet,  in  order  to  avoid  all  danger  of  "beards"  in  cutting 
•wood  sections,  procured  a  knife  with  a  semicircular  blade.  This  was 
fastened  at  the  end  upon  a  flat  plate,  in  order  to  revolve,  as  we  may 
call  it,  the  handle  being  long  enough  to  give  leverage  for  any  required 
power.  The  wood  supporter  being  placed  in  a  favourable  position, 
the  knife  is  easily  brought  round,  and  the  section  cut  by  a  circular 
action. 


154  PREPARATION  AND   MOTTXTIXG 

the  same  length  of  time,  so  as  to  soften  and  render  it  easy 
to  cut.  Sections  may  then  be  obtained  in  the  manner  just 
described,  but  they  often  curl  to  such  a  degree  from  their 
previous  immersion  in  water  as  to  render  pressure  necessary 
to  flatten  them  until  dry.  They  are  often  mounted  dry, 
and  require  no  care  beyond  other  objects,  as  in  Chapter 
III.  Some,  however,  are  best  mounted  in  balsam,  par- 
ticularly the  long  sections  when  used  for  the  polariscope ; 
these  must  be  soaked  in  turpentine,  and  the  greatest  care 
taken  that  all  air-bubbles  are  removed.  Others  are  thought 
to  be  most  useful  when  mounted  in  shallow  cells  with  some  of 
the  preservative  liquids  mentioned  in  Chapter  "V. — weak 
spirit  and  water,  chloride  of  calcium  solution  of  the  strength 
of  one  part  of  the  salt  to  three  parts  of  distilled  water,  &c. 

The  above  "  section-cutter"  may  not  be  within  the  reach 
of  every  student,  nor  is  it  absolutely  necessary ;  though  where 
any  great  number  of  specimens  is  required  it  is  very  useful, 
and  insures  greater  uniformity  in  the  thickness.  Many 
employ  a  razor  for  the  purpose,  which  must  always  be  kept 
sharp  by  frequent  stropping.  Sections  of  leaves  also  may 
be  procured  by  the  same  means,  though,  as  before  mentioned, 
they  are  sometimes  divided  by  stripping  the  coatings  off 
with  the  fingers.  The  cells  which  come  to  sight  by  cutting 
some  of  the  orchideous  plants  are  most  interesting.  To  cut 
these  leaves  they  may  be  laid  upon  a  flat  piece  of  cork,  thus 
exposing  the  razor  to  no  danger  of  injury  by  coming  in 
contact  with  the  support.  It  may  be  mentioned  here  that 
the  razor  may  also  be  used  in  cutting  sections  of  the  rush, 
than  which  a  more  beautiful  object  can  scarcely  be  found 
when  viewed  transversely,  as  it  shows  the  stellate  arrange- 
ments of  the  parenchyma.  This  should  be  mounted  dry. 
In  the  same  way  sections  of  the  leaf-stalks  of  ferns  may  also 
be  cut,  some  of  which,  as  Dr.  Carpenter  states,  show  the 
curious  ducts  very  beautifully,  especially  when  cut  rather 
obliquely. 

It  has  been  found  a  ready  method  of  cutting  sections  of 
the  rush  and  such  like  plants,  to  suck  a  solution  of  gum  up 


OF  MICROSCOPIC  OBJECTS.  155 

into  the  pith,  and  when  this  is  dry  thin  sections  could  be 
cut  and  the  gum  washed  out  again,  and  these  could  be 
mounted  in  balsam. 

The  plan  adopted  by  most  practical  histologists  for  cut- 
ting sections  of  soft  tissues  is  as  follows  : — The  tissue  to  be 
cut  is  first  hardened  by  immersion  in  a  chromic  acid  solu- 
tion varying  in  strength  from  0'25  to  2  per  cent.,  or  by  im- 
mersion in  alcohol.  The  substance  to  be  cut  may  then  be 
embedded  in  melted  wax  and  spermaceti,  in  proportions 
suitable  to  the  nature  of  the  substance  to  be  cut ;  when 
this  is  cold  the  section  may  be  cut  with  a  razor  ground 
flat  on  one  side,  and  may  then  be  floated  off  in  spirits  of 
wine. 

These  sections  mount  very  well  in  Canada  balsam,  if 
after  being  removed  from  the  spirit  they  are  immersed  in 
oil  of  cloves  till  they  become  clear,  then  put  into  turpentine 
before  the  balsam.  The  thinness  of  the  se'ction  will  depend 
very  much  on  the  dexterity  of  the  operator,  but  section- 
cutting  instruments  for  soft  tissues  can  now  be  obtained  at 
most  scientific  instrument  shops. 

When  sections  of  softer  substances  are  required,  no  instru- 
ment can  be  compared  with  "  Valentin's  knife,"  which  con- 
sists of  two  steel  blades  lying  parallel  with  each  other  and 
attached  at  the  lower  end.  The  distance  of  separation  may 
be  regulated  at  will  by  a  small  screw  near  the  handle. 
When,  therefore,  a  section  is  wanted,  the  substance  must 
be  cut  through,  and  betwixt  the  blades  a  thin  strip  will  be 
found,  which  may  be  made  of  any  thickness,  according  to 
the  distance  of  their  separation.  By  loosening  the  screw 
the  blades  may  be  extended,  and  the  section  may  be  floated 
out  in  water  if  the  damp  will  not  injure  it.  The  knife  cuts 
much  better  if  dipped  in  water  or  glycerine  immediately  be- 
fore use,  and  also  when  the  substance  to  be  operated  upon 
is  wet,  or  even  under  water  altogether ;  but  care  must  be 
taken,  after  use,  to  clean  the  blades  thoroughly  and  oil  them 
before  laying  by,  if  the  place  is  at  all  damp.  This  instru- 
ment is  most  useful  in  such  subjects  as  anatomical  prepara- 


156  PREPARATION  AND   MOUNTING 

tions  where  the  sections  are  required  to  show  the  position  of 
the  different  vessels,  &c. ;  but,  as  before  stated,  is  very  valu- 
able for  all  soft  substances.  As  an  instance  of  this,  it  may 
be  mentioned,  that  it  is  frequently  used  iii  cutting  sections 
of  sponges  ;  but  as  these  are  often  very  full  of  spicula, 
it  is  much  better  to  press  the  sponge  flat  until  dry,  and  then 
cut  off  thin  shavings  with  a  very  sharp  knife ;  these  shav- 
ings will  expand  when  placed  in  water.  After  this  they 
may  be  laid  betwixt  two  flat  surfaces  and  dried,  when  they 
may  be  mounted  as  other  dry  objects,  or,  when  desirable,  in 
balsam. 

Valentin's  "knife  is  very  much  used  in  taking  sections  of 
skin,  which  are  afterwards  treated  with  potash  solution, 
acids,  &c.,  to  bring  out  in  the  best  way  the  different  por- 
tions. Dr.  Lister's  mode,  however,  of  getting  these  is  thus 
given  in  the  Microscopic  Journal : — "  But  I  afterwards 
found  that  much  better  sections  could  be  obtained  from 
dried  specimens.  A  portion  of  shaved  scalp  being  placed 
between  two  thin  slips  of  deal,  a  piece  of  string  is  tied 
round  them  so  as  to  exercise  a  slight  degree  of  compression  ; 
the  preparation  is  now  laid  aside  for  twenty-four  hours, 
when  it  is  found  to  be  dried  to  an  almost  horny  condition. 
It  then  adheres  firmly  by  its  lower  surface  to  one  of  the 
slips,  and  thus  it  can  be  held  securely,  while  extremely  thin 
and  equable  sections  are  cut  with  great  facility  in  any  plane 
that  may  be  desired.  These  sections,  when  moistened  with 
a  drop  of  water  and  treated  with  acetic  acid,  are  as  well 
suited  for  the  investigation  of  the  muscular  tissue  as  if  they 
had  not  been  dried." 

There  are  many  who  almost  confine  their  attention  to 
polarized  light  and  its  beautiful  effects.  Such  would  not 
deem  these  efforts  to  aid  the  student  in  cutting  sections 
complete,  without  some  notice  of  those  which  are  taken 
from  various  crystals,  in  order  to  display  that  curious  and 
beautiful  phenomenon,  the  rings  with  a  cross.  The  arrange- 
ment of  these  is  somewhat  changed  by  the  crystal  which 
affords  the  section ;  but  nitrate  of  potash  gives  two  sets  of 


OF   HICKOSCOPIC   OBJECTS.  157 

rings  with  a  cross,  the  long  line   of  which  passes  through 
both,  the  short  line  dividing  it  in  the  middle. 

The  process  of  cutting  these  sections  is  rather  difficult, 
but  a  little  care  and  perseverance  will  conquer  all  this.  The 
following  is  extracted  from  the  Encyclopaedia  Metropolitana : 
"  Nitre  crystallizes  in  long  six-sided  prisms  whose  section, 
perpendicular  to  their  sides,  is  the  regular  hexagon.  They 
are  generally  very  much  interrupted  in  their  structure ;  but 
by  turning  over  a  considerable  quantity  of  the  ordinary 
saltpetre*  of  the  shops  specimens  are  readily  found  which 
have  perfectly  transparent  portions  of  some  extent.  Select- 
ing one  of  these,  cut  it  with  a  knife  into  a  plate  above  a 
quarter  of  an  inch  thick,  directly  across  the  axis  of  the 
prism,  and  then  grind  it  down  on  a  broad  wet  file  till  it 
is  reduced  to  about  one  quarter  or  a  sixth  of  an  inch  thick, 
smooth  the  surface  on  a  wet  piece  of  emeried  glass,  and 
polish  on  a  piece  of  silk  strained  very  tight  over  a  strip  of 
plate-glass,  and  rubbed  with  a  mixture  of  tallow  and  colco- 
thar  of  vitriol.  This  operation  requires  practice.  It  cannot 
be  effected  unless  the  nitre  be  applied  wet  and  rubbed  till 
quite  dry,  increasing  the  rapidity  of  the  friction  as  the 
moisture  evaporates.  It  must  be  performed  in  gloves,  as 
the  vapour  from  the  fingers,  as  well  as  the  slightest  breath, 
dims  the  polished  surface  effectually.  With  these  precau- 
tions a  perfect  vitreous  polish  is  easily  obtained.  We  may 
here  remark,  that  hardly  any  two  salts  can  be  polished  by 
the  same  process.  Thus,  Rochelle  salt  must  be  finished  wet 
on  the  silk,  and  instantly  transferred  to  soft  bibulous  linen 
and  rapidly  rubbed  dry.  Experience  alone  can  teach  these 
peculiarities,  and  it  is  necessary  to  resort  to  contrivances 
(sometimes  very  strange  ones)  for  the  purpose  of  obtaining 
good  polished  sections  of  soft  crystals,  especially  of  those 
easily  soluble  in  water. 


*  Sometimes  the  saltpetre  of  the  shops  is  nitrate  of  soda,  and  as 
this  is  slightly  deliquescent,  it  is  well  to  be  certain  that  we  have  the 
nitrate  of  potash,  which  is  free  from  this  defect. 


158  PREPARATION  AND   MOUNTING 

"  The  nitre  is  thus  polished  on  both  its  surfaces,  which 
should  be  brought  as  near  as  possible  to  parallelism." 

Some  sections  of  the  naturally  formed  crystals  also  show 
the  "  rings "  very  well, — as  Iceland  spar,  which  gives  a 
single  ring  and  cross ;  but  the  difficulty  of  cutting  and 
polishing  them  is  almost  too  great  for  the  amateur,  and 
must  be  left  to  the  lapidary.  This  curious  phenomenon, 
however,  may  be  seen  by  using  a  plate  of  ice  uninterruptedly 
formed  of  about  one  inch  in  thickness. 

Before  concluding  bhese  remarks  on  sections,  I  must  men- 
tion a  few  difficulties  which  may  be  met  with,  and  their 
remedies.  The  foremost  of  these  is  the  softness  of  some 
objects,  which  have  not  resistance  enough  in  themselves  to 
bear  cutting  even  with  the  sharpest  instruments.  This  may 
often  be  removed  by  soaking  in  a  solution  of  gum,  and  then 
drying,  which  will  render  the  substance  firm  enough  to  be 
cut,  when  the  sections  must  be  steeped  in  water,  and  the 
gum  thus  removed.  Small  seeds,  &c.,  may  be  placed  in 
wax  when  warmed,  and  will  be  held  firmly  enough  when  it 
is  again  cold  to  allow  of  them  being  cut  into  sections.* 
And,  lastly,  where  a  substitute  for  a  microscopist's  hand- 
vice  13  required,  a  cork  which  fits  any  tube  large  enough 
may  be  taken  and  split,  the  object  being  then  placed  between 
the  two  parts,  and  the  cork  thrust  into  the  tube,  a  sufficient 
degree  of  firmness  will  be  obtained  to  resist  any  necessary 
cutting. 

*  Mr.  T.  K.  Parker  informs  ma  that  he  uses  paraffine  as  an  "  ob- 
ject-support"  when  sections  are  required,  as  follows  : — "The  mixture 
I  use  for  embedding  objects  consists  of  solid  paraffine  (ordinary  paraf- 
fine candles  will  do  very  well)  melted  down  and  mixed  with  a  little 
paraffine  oil,  without  which  the  paraffine  is  too  hard  to  be  easily  cut. 
The  mixture  when  cold  is  cut  into  suitable  pieces,  a  hole  is  scooped 
out  in  the  centre,  the  object  to  be  cut  placed  in  it,  and  a  little  of  the 
melted  mixture  poured  round  it.  The  sections  are  cut  with  an  ordi- 
nary razor,  which,  as  well  as  the  object,  must  be  continually  wetted 
•with  spirit.  This  method  is  useful  for  all  objects  which  are  either  too 
small  for  the  hand  or  too  soft  or  brittle  to  be  cut  in  the  ordinary  way. 
It  is  especially  useful  for  histological  specimens,  leaves,  embryos, 
&c." 


OP  MICROSCOPIC   OBJECTS.  '  159 

The  ether  process  of  drying  tissues  haa  been  described  by 
Mr.  Suffolk,  at  a  meeting  of  the  Quekett  Microscopical 
Club,  and  was  communicated  by  Mr.  Crocker  to  him — it  is 
as  follows  : — A  wide-mouthed  well-stoppered  bottle  must  be 
selected.  At  the  bottom  is  placed  a  slice  from  the  bowl  of 
a  tobacco-pipe,  forming  a  support  for  a  Berlin  crucible  with 
its  cover.  A  quantity  of  fused  chloride  of  calcium  in  frag- 
ments is  placed  at  the  bottom  of  the  bottle,  which  is  nearly 
filled  with  pure  ether,  so  that  the  crucible  may  be  covered. 
The  tissue  to  be  dried  is  placed  in  the  crucible,  and  is  covered, 
if  necessary  to  keep  it  from  floating,  by  a  piece  of  glass. 
The  ether  takes  water  from  the  tissue,  and  the  chloride 
again  takes  it  from  the  ether ;  so  that  the  section  is  thus 
gradually  dried,  and  with,  as  little  shrinking  as  possible, 
however  delicate  it  may  be.  This  process  is  most  fitted  for 
the  preparation  of  succulent  roots,  tubers,  or  stems,  and  in- 
deed is  only  fit  for  those  tissues  which  are  not  injured  by 
immersion  in  ether,  or  dissolved  by  it,  such,  as  fat,  &c.,  or 
colouring  matter. 

DISSECTION. — As  I  stated  at  the  commencement  of  this 
chapter,  no  written  instructions  can  enable  any  student  to 
become  an  adept  in  this  branch  without  much  experience 
and  no  little  study.  I  will,  however,  describe  the  necessary 
apparatus,  and  afterwards  mention  the  mode  of  treatment 
which  certain  objects  require. 

A  different  microscope  is  manufactured  for  the  purpose 
of  dissection,  most  first-rate  makers  having  their  own  model. 
The  object-glasses  of  many  of  these  are  simple,  and  conse- 
quently not  expensive ;  but  one  of  the  great  requisites  is  a 
stage  large  enough  to  hold  the  trough,  in  which  the  opera- 
tion is  often  performed.  "Where  this  is  the  case  it  would 
scarcely  be  worth  the  expense  of  getting  a  dissecting  micro- 
scope if  the  student  were  pursuing  no  particular  study, 
but  merely  used  the  instrument  when  an  object  to  be 
operated  upon  turned  up  accidentally.  The  ordinary  form 
is  much  improved  for  this  purpose,  by  having  two  wooden 
rests  placed  at  the  sides  of  th»  microscope,  upon  which  the 


160  PREPARATION   AND   MOUNTING 

hands  may  be  supported  when  working  upon  the  stage. 
They  should  be  weighty  enough  to  be  free  from  danger  of 
moving.  These  supports  will  also  be  found  to  remedy 
much  of  the  weariness  which  inevitably  arises  from  having 
to  sustain  the  hands  as  well  as  work  with  them.  The 
erector,  as  I  before  observed,  is  necessary  to  a  young  student; 
but  with  a  little  practice  he  may  work  very  well  without  it. 

We  will  now  notice  some  of  the  instruments  which  are 
most  useful  in  dissection.  Two  or  three  different  sizes  of 
ordinary  scissors  should  be  possessed,  but  the  shapes  must 
be  as  modified  in  others  for  many  purposes,  as  those  used  by 
surgeons ;  a  pair  with  the  cutting  parts  bent  in  a  hori- 
zontal direction,  and  another  pair  slightly  curved  in  a 
perpendicular ;  so  that  parts  of  the  substance  operated  upon 
may  be  reached,  which  it  would  be  impossible  to  touch  with 
straight  scissors.  One  point  of  these  is  sometimes  blunt, 
and  the  other  acute,  being  thus  made  very  useful  in  opening 
tubular  formations.  Another  form  of  these  is  made,  where 
the  blades  of  the  scissors  are  kept  open  by  a  spring,  the 
handles  being  pressed  together  by  the  fingers.  Where  it  is 
desirable,  one  or  both  of  these  handles  may  be  lengthened  to 
any  degree  by  the  addition  of  small  pieces  of  wood. 

THE  KNIVES  which  are  most  useful  are  those  of  the 
smallest  kind  which  surgeons  employ  in  very  delicate  opera- 
tions. These  are  made  about  the  length  of  an  ordinary 
pen-knife,  and  are  fixed  in  rather  long  flattish  handles ; 
some  are  curved  inwards,  like  the  blade  of  a  scythe,  others 
backwards  ;  some  taper  to  a  point,  whilst  others  again  are 
broad  and  very  much  rounded.  Complete  boxes  are 
now  fitted  up  by  the  cutlers,  of  excellent  quality  and  sur- 
prisingly cheap. 

NEEDLES. — These  are  very  useful  and  should  be  firmly 
fixed  in  handles  as  recommended  in  Chapter  II.  It  is  con- 
venient to  have  them  of  various  lengths  and  thicknesses.  If 
curved  by  heating  and  bending  to  any  required  shape  they 
may  be  re-hardened  by  putting  them  whilst  hot  into  cold 
water.  Dr.  Carpenter  also  makes  edged  instruments  by 


OF   MICROSCOPIC    OBJECTS,  16] 

rubbing  down  needles  upon  a  hone.  They  are  more  pleasant 
to  work  with  when  short,  as  the  spring  they  have  whilst 
long  robs  them  of  much  of  their  firmness.  Glass  points 
made  by  drawing  out  glass  rods  to  a  point  will  be  found 
useful  in  manipulating  with  acids. 

A  glass  syringe  is  also  useful  in  many  operations,  serving 
not  only  to  cleanse  the  objects  but  to  add  to,  or  withdraw 
liquids  from,  the  dissecting-trough.  This  trough  will  now  be 
described,  as  many  substances  are  so  changed  by  becoming 
dry  that  it  is  impossible  to  dissect  them  unless  they  are 
immersed  in  water  during  the  operation.  If  the  object  be 
opaque  and  must  be  worked  by  reflected  light,  a  small  square 
trough  may  be  made  to  the  required  size,  of  gutta-percha, 
which  substance  will  not  injure  the  edge  of  the  knives,  &c. ; 
but  where  transparency  is  necessary,  a  piece  of  thin  plate- 
glass  must  be  taken,  and  by  the  aid  of  marine-glue  (as 
explained  in  Chapter  V.)  sides  affixed  of  the  required 
depth.  As  pins,  &c.,  cannot  be  used  with  the  glass  troughs 
and  the  substance  must  be  kept  extended,  a  thin  sheet  of 
cork  loaded  with  lead  in  order  to  keep  it  under  water  may 
be  used ;  but  this,  of  course,  renders  the  bottom  opaque. 
When  working  with  many  thin  substances,  a  plate  of  glass 
three  or  four  inches  long  and  two  wide  will  serve  every 
purpose,  and  be  more  pleasant  to  use  than  the  trough.  A 
drop  or  two  of  water  will  be  as  much  liquid  as  is  needed, 
and  this  will  lie  very  well  upon  the  flat  surface.  As  these 
are  the  principal  apparatus  and  arrangements  which  are 
requisite  in  dissection,  the  method  of  proceeding  in  a  few 
cases  may  now  be  noticed. 

VEGETABLES. — The  dissection  of  vegetable  matter  is  much 
less  complicated  than  that  of  animal ;  maceration  in  water 
being  a  great  assistant,  and  in  many  cases  removing  all 
necessity  for  the  use  of  the  knife,  especially  if  hot  water  can 
be  used  without  injury  to  the  objects,  as  is  the  case  with 
many.  This  maceration  may  be  assisted  by  needles,  and 
portions  of  the  matter  which  are  not  required  may  be  re- 
moved by  them.  When,  for  instance,  the  spiral  vessels 


162  PREPARATION    AND   MOUKTIXG 

which  are  found  in  rhubarb  are  wanted,  some  parts  con- 
taining these  are  chosen  and  left  in  a  small  quantity  of 
water  until  the  mass  becomes  soft,  and  this  is  more  quickly 
effected  when  the  water  is  not  changed.  The  mass  must  be 
then  placed  upon  a  glass  plate  when  practicable,  or  in  the 
trough  when  large,  and  with  the  aid  of  two  needles  the 
matter  may  be  removed  from  the  spiral  vessels,  which  are 
plainly  seen  with  a  comparatively  low  power ;  and  by  con- 
veying these  to  a  clean  slip  of  glass,  repeating  the  process, 
and  at  last  washing  well,  good  specimens  may  be  procnred. 
Most  of  these  should  be  mounted  in  some  of  the  preservative 
liquids  in  the  manner  described  in  Chapter  V.  Many, 
however,  may  be  dried  on  the  slide,  immersed  in  turpentine, 
and  then  mounted  in  balsam  ;  but  liquid  is  preferable,  as  it 
best  preserves  their  natural  appearance.  Certain  kinds  of 
vegetables  require  a  different  treatment  to  eeparate  these 
spiral  vessels.  Asparagus  is  composed  of  very  hard  vegetable 
matter,  and  some  have  recommended  the  stems  to  be  first 
boiled,  which  will  soften  them  to  such  a  degree  that  they 
may  easily  be  separated.  Dilute  acids  are  also  occasionally 
used  to  effect  this ;  and  in  some  instances  to  obtain  the 
raphides  caustic  potash  may  be  employed ;  but  after  any  of 
these  agents  have  been  used,  the  objects  must  be  thoroughly 
cleansed  with  water,  else  the  dissecting  instruments  (and 
perhaps  the  cell)  will  be  injured  by  the  action  of  the  re- 
maining portion  of  the  softening  agent. 

For  the  dissection  of  animal  tissues  it  is  necessary  that 
the  instruments  be  in  the  best  order  as  to  sharpness,  &c. ; 
and  as  the  rules  to  be  observed  must  necessarily  be  some- 
what alike  in  many  instances,  the  treatment  required  by 
some  of  the  objects  most  frequently  mounted  will  now  be 
described.  We  may  here  remark  that  cartilage  can  be 
best  examined  by  taking  sections  which  will  show  the  ar- 
rangement of  the  cells  very  perfectly.  This,  however,  is 
plainly  seen  in  the  mouse's  ear  without  any  section  being 
necessary.  Glycerine,  the  preservative  liquids  before  men- 
tioned, and  Canada  balsam  are  all  used  to  mount  it 


OF   MICROSCOPIC   OBJECTS.  163 

but  perhaps  the  first-named  may  be  preferred  in  many 
cases. 

Before  treating  of  separate  objects  it  will  be  well  to  notice 
what  M.  Brunetti  has  said  on  preparing  anatomical  speci- 
mens. The  process  consists  of  four  stages — viz.,  washing, 
divesting  of  fat,  treating  with  tannin,  and  desiccation.  A 
stream  of  pure  water  is  injected  throngh  the  blood-vessels 
and  secretory  ducts  of  the  part  to  be  preserved ;  the  water 
is  afterwards  expelled  by  means  of  alcohol.  To  remove  the 
fat,  the  vessels  are  in  like  manner  injected  with  ether, 
which  penetrates  the  tissues  and  dissolves  all  the  fatty 
matters.  These  operations  occupy  about  two  hours,  and 
the  object  thus  prepared  may  then  be  kept  for  a  long  time 
in  ether,  if  desired.  A  solution  of  tannin  is  next  injected 
in  a  similar  manner,  and  the  ether  washed  out  by  a  stream 
of  pure  water.  The  preparation  is  then  placed  in  a  double- 
bottomed  vessel  containing  boiling  water — a  sort  of  bain- 
marie — in  order  to  displace  the  fluid  previously  used  by 
dry  heated  air.  Air  compressed  in  a  reservoir  to  about 
two  atmospheres  is  forced  into  the  vessels  and  ducts 
through  heated  tubes  containing  chloride  of  calcium  :  all 
moisture  is  thus  expelled  and  the  process  is  completed. 
The  preparation  thus  treated  is  light,  and  retains 
its  volume,  its  normal  consistence,  and  all  its  histological 
elements. 

MUSCLE. — This  is  what  is  commonly  called  the  flesh 
of  animals.  If  a  piece  be  laid  upon  the  slide  under  the 
microscope,  bundles  of  fibres  will  be  perceived,  which  with 
needles  and  a  little  patience  may  be  separated  into  portions, 
some  of  these  being  striated,  or  marked  with  alternate  spaces 
of  dark  and  light.  Some  of  the  non-striated  or  smooth  class 
of  muscle,  such  as  is  found  in  intestines,  may  be  prepared 
for  the  microscope  by  immersing  for  a  day  or  two  in  nitric 
acid  diluted  with  three  or  four  parts  of  water,  and  then 
separating  with  needles  and  mounting  as  soon  as  possible. 
Sometimes  boiling  is  resorted  to  to  facilitate  the  separa- 
tion, and  occasions  little  or  no  alteration  in  the  material. 
M  2 


164  PBEPABATION   AND    MOUNTING 

Specimens  are  often  taken  from  the  frog  and  the  pig,  as 
being  amongst  the  best,  Goadby's  Solution  being  generally 
used  in  mounting  them.  The  muscles  of  insects  also  show 
the  strias  very  perfectly. 

NERVE-TISSUE. — This  is  seldom  mounted;  as  Dr.  Carpenter 
observes,  "  no  method  of  preserving  the  nerve-tissue  has 
been  devised  which  makes  it  worth  while  to  mount  pre- 
parations for  the  sake  of  displaying  its  minute  characters," 
but  we  will  mention  a  few  particulars  to  be  observed  in  its 
treatment.  The  nerve  should  be  taken  from  the  animal  as 
soon  as  possible  after  death,  and  laid  upon  a  glass  slide, 
with  a  drop  or  two  of  serum  if  possible.  The  needles  may 
be  used  to  clean  it,  but  extreme  delicacy  is  necessary.  It 
will  be  found  that  the  nerve  is  tubular  and  filled  with  a 
substance  which  is  readily  ejected  by  very  slight  pressure. 
When  the  nerve  is  submitted  to  the  action  of  acetic  acid, 
the  outer  covering,  which  is  very  thin,  is  considerably  con- 
tracted, whilst  the  inner  tube  is  left  projecting ;  and  thus  is 
most  distinctly  shown  the  nature  of  the  arrangement.  Dr. 
Lockhart  Clarke,  who  has  made  great  researches  into  the 
structure  of  the  spinal  cord,  gives  a  part  of  his  experience 
as  follows  : — He  takes  a  perfectly  fresh  spinal  cord  and 
submits  it  to  the  action  of  strong  spirits  of  wine.  This 
gives  the  substance  such  a  degree  of  hardness  that  thin 
sections  may  be  readily  cut  from  it,  which  should  be  placed 
upon  a  glass  in  a  liquid  consisting  of  three  parts  of  spirit 
and  one  of  acetic  acid,  which  renders  them  very  distinct. 
M.  Grandry  has  treated  nerve-tissue  thus  : — Taking 
portions  of  nervous  tissue  obtained  from  the  frog  and  rabbit, 
he  placed  them  in  a  one-fourth  per  cent,  solution  of  nitrate 
of  silver  in  pure  water,  macerating  them  for  five  days  in  the 
dark,  and  then  exposing  them  for  three  days  to  bright  light. 
If  the  surface  of  the  cord  thus  treated  be  carefully  teazed 
out  with  needles,  the  axis-cylinders  are  found  to  exhibit  a 
very  regular  and  sharply  defined  transverse  striation — clear, 
unstained  stria?  alternating  with  deeply  tinted  ones.  Dr. 
Bastian  recommends  us  to  mount  delicate  specimens  of 


OF   MICKOSCOPIC   OBJECTS.  1G5 

nerve-tissue  in  a  mixture  of  glycerine  and  carbolic  acid  in 
the  proportion  of  fifteen  of  the  first  to]  one  of  the  second. 
To  mount  these  sections,  they  must  now  be  steeped  in  pure 
spirit  for  two  hours,  and  afterwards  in  oil  of  turpentine,  and 
lastly  must  be  mounted  in  Canada  balsam. 

Dr.  Lionel  Beale  recommends  the  use  of  chloride  of  gold 
for  colouring  nerve  fibres.  A  solution  containing  from  2  to 
1  per  cent,  in  distilled  water  should  be  made.  The  tissue 
having  been  soaked  in  it  until  it  becomes  straw-coloured,  is 
to  be  washed,  and  then  placed  in  very  dilute  acetic  acid 
containing  one  per  cent,  or  less.  The  nerves  exhibit  a  blue 
or  violet  tinge  on  exposure  to  light  for  a  few  hours.  He 
speaks  also  of  solution  of  osmic  acid  for  the  same  purpose, 
1  part  to  100  of  water,  but  not  with  much  approval.  The 
aniline  colours,  such  as  magenta  and  solferino,  may,  accord- 
ing to  the  same  authority,  be  also  employed  for  most  tissues. 
They  are  not  very  soluble  in  water,  but  are  readily  dissolved 
by  alcohol.  A  grain  of  the  colour,  10  to  15  minims  of 
alcohol,  and  an  ounce  of  distilled  water,  make  a  dark  red  or 
blue  (purple)  solution  which  colours  tissues  very  readily. 
For  these  and  many  other  useful  formulas  for  the  same  pur- 
pose, the  reader  may  consult  "  Beale  on  the  Microscope." 

Dr.  Klein,  in  No.  40  of  the  Monthly  Microscopical  Journal, 
in  order  to  demonstrate  the  nerves  of  the  cornea,  takes  that 
of  the  rabbit  or  guinea-pig,  a  quarter  or  half  an  hour  after 
death,  and  places  it  in  a  half  per  cent,  solution  of  chloride 
of  gold,  for  from  one  and  a  half  to  two  hours — that  of  the 
guinea-pig  for  an  hour  to  an  hour  and  a  quarter.  After 
that,  the  cornea  is  washed  in  distilled  water,  and  exposed  to 
the  light  in  distilled  water  for  from  24  to  36  hours  (the 
water  being  changed  twice,  or  oftener).  After  this  time  has 
elapsed,  the  cornea  is  transferred  into  a  mixture  of  one  part 
pure  glycerine  and  two  of  distilled  water,  where  it  remains 
for  two  or  three  days.  Up  to  this  time  the  cornea  has  not 
assumed  a  darker  colour  than  ash-grey,  perhaps  having  a 
violet  tint ;  at  all  events  the  whole  of  the  cornea  is  trans- 
parent. It  is  then  brushed  over  on  its  anterior  surface 


163  PREPARATION   AND   MOUNTING 

under  water  with  a  fine  camel-hair  brush  very  gently,  so  as 
to  remove  the  precipitates  of  the  gold  salt.  Sections  of  a 
cornea  so  prepared  may  be  made  on  the  finger  by  a  sharp 
razor,  and  must  be  examined  and  kept  in  glycerine. 

LIVER,  KIDNEY,  SPLEEN,  LUNG,  &c. — Some  parts  which 
are  too  soft  to  be  cut  into  sections  in  their  ordinary  state, 
are  usually  hardened  by  being  steeped  in  a  solution  of 
chromic  acid,  about  two  grains  to  an  ounce  of  water.  This 
will  take  some  weeks  according  to  the  substance,  and  the 
solution  should  be  changed  now  and  then.  Dr.  Bastian,  for 
mounting,  uses  Canada  balsam  partially  dried  to  dispel  the 
turpentine,  and  then  diluted  to  necessary  consistence  with 
benzole.  The  section  being  cut  from  the  hardened  organ  is 
washed  in  spirits  of  wine  for  some  minutes,  then  a  drop  of 
liquid  carbolic  acid  is  placed  on  the  slide  where  the  speci- 
men is  to  be  mounted.  Take  the  specimen  and  let  its  edge 
touch  a  piece  of  blotting-paper,  and  place  it  upon  the 
carbolic  acid,  which  will  render  a  thin  section  transparent 
in  about  a  minute.  Remove  the  superfluous  acid  with 
blotting-paper,  when  two  or  three  drops  of  chloroform  must 
be  poured  upon  the  section  and  remain  one  minute.  Drain 
off  and  place  upon  the  object  the  solution  of  Canada  balsam 
in  benzole,  and  apply  the  thin  glass  cover.  Or  place  the 
object  in  ordinary  spirits  of  wine  for  about  a  minute  to  wash 
it,  then  remove  into  absolute  alcohol  for  five  minutes.  Lay 
it  upon  the  slide  and  drain,  cover  with  one  or  two  drops  of 
benzole  for  about  a  minute,  tilt  to  drain  off,  and  proceed  as 
above. 

Both  these  methods  are  good,  but  the  first  does  not 
always  answer  for  sections  of  liver,  as  they  generally  are 
acted  upon  by  carbolic  acid;  but  few  other  tissues  are  thus 
affected.  Tinted  specimens  seem  equally  safe  when  mounted 
in  this  way. 

SECTIONS  or  BRAIN  AND  SPINAL  CORD. — Dr.  Bastian 
gives  his  experience  of  these  tissues  as  follows  : — I  immerse 
the  section  for  about  ten  minutes  in  absolute  alcohol  diluted 
with  eight  per  cent,  of  water,  then  place  upon  the  glass 


OP  MICBOSCOPIC   OBJECTS.  167 

slide,  and  before  it  becomes  dry  pour  over  it  two  or  three 
drops  of  pyroacetic  acid  for  about  half  a  minute.  Tilt  this 
off  and  replace  by  chloroform.  Watch  the  effects,  as  before, 
under  the  microscope,  and  then  cover  with  the  Canada 
balsam  solution  and  finish.  These  specimens,  however,  are 
not  always  permanent  in  their  appearance,  according  to  the 
results  of  some. 

Mr.  Alfred  Sanders  gives  his  experience  as  differing  some- 
what from  this.  He  says — The  brain,  or  other  structure, 
being,  as  usual,  hardened  in  chromic  acid,  the  section  is  put 
for  a  short  time  in  spirits  of  wine,  and  thence  transferred  to 
the  creosote,  which  makes  it  transparent  in  a  few  minutes, 
when  it  is  placed  in  Canada  balsam.  The  balsam  will  mix 
easily  with  the  creosote,  or  the  solution  in  benzole  may  be 
employed. 

TBACHE^E  OF  INSECTS,  &o.  —  The. nature  of  these  was  de- 
scribed in  Chapter  IV.,  but  the  method  of  procuring  them 
was  not  explained,  as  this  clearly  belongs  to  dissection. 
The  larger  tubes  are  readily  separated  by  placing  the  insect 
in  water,  and  fixing  as  firmly  as  possible,  when  the  body 
must  be  opened  and  the  viscera  removed.  The  tracheae  may 
then  be  cleaned  by  the  aid  of  a  camel-hair  pencil,  and 
floated  upon  a  glass,  where  they  must  first  be  allowed  to  dry, 
and  then  be  mounted  in  balsam.  Mr.  Quekett  gives  the 
following  method  of  removing  the  tracheas  from  the  larva  of 
an  insect : — "  Make  a  small  opening  in  its  body,  and  then 
place  it  in  strong  acetic  acid.  This  will  soften  or  decompose 
all  the  viscera,  and  the  tracheae  may  then  be  well  washed 
with  the  syringe,  and  removed  from  the  body  with  the 
greatest  facility,  by  cutting  away  the  connections  of  tho 
main  tubes  with  the  spiracles  by  means  of  fine-pointed 
scissors.  In  order  to  get  them  upon  the  slide,  it  must  bo 
put  into  the  fluid,  and  the  tracheae  floated  upon  it ;  after 
which  they  may  be  laid  out  in  their  proper  position,  then 
dried  and  mounted  in  balsam."  If  we  wish  them  to  bear 
their  natural  appearance,  they  must  be  mounted  in  a  cell 
with  Goadby'd  fluid ;  but  the  structure  is  sometimes 


168  PREPARATION   AND   MOUNTING 

shown  in  specimens  mounted  dry.  As  before  mentioned, 
these  tracheo3  terminate  on  the  outside  in  openings  termed 
spiracles,  which  are  round,  oblong,  and  of  various  shapes. 
Over  these  are  generally  a  quantity  of  minute  hairs,  forming  a 
guard  against  the  entrance  of  dust.  The  forms  of  these  are 
seldom  alike  in  two  different  kinds  of  insects,  so  that  there 
is  here  a  wide  field  for  the  student.  The  dissection,  more- 
over, is  very  easy,  as  they  may  be  cut  from  the  body  with 
a  sharp  knife  or  scissors,  and  mounted  in  balsam  or  fluid. 
Many  of  the  larvas  afford  good  specimens,  as  do  also  some 
of  the  common  Coleopterous  insects.  Perhaps,  no  more 
satisfactory  object  can  be  met  with  to  give  the  student  good 
examples  of  spiracles  than  the  water-beetle  Dytiscus,  before 
mentioned,  as  affording  such  perfectly  beautiful  suckers. 
They  will  be  found  to  vary  in  appearance  according  to  the 
part  of  the  body  from  which  they  are  taken  ;  but  all  are 
equally  interesting. 

Mr.  Lewis  Gr.  Mills,  LL.B.,  gives  the  following  account  of 
his  extracting  the  poison  glands  from  a  spider : — Having 
killed  a  large  spider  with  chloroform,  I  left  it  in  water  for 
seven  or  eight  days.  This  treatment  usually  softens  the 
outer  skin  of  insects  and  causes  the  viscera  to  swell,  so  as 
to  burst  through  the  outer  integument,  and  it  is  in  this 
state,  perhaps,  that  the  poison  glands  are  most  easily  dis- 
covered and  traced  to  their  points  of  attachment,  I  then 
drew  the  mandibles  from  the  body,  and,  having  placed 
them  with  a  little  water  on  a  slide  and  covered  them  with  a 
piece  of  thin  glass,  I  found  that,  upon  the  application  of 
pressure,  the  two  glands  shot  out  and  protruded  from  the 
bases  of  the  mandibles.  I  tore  open  one  of  the  mandibles 
with  needles,  so  as  to  disturb  the  gland  as  little  as  possible. 
The  gland  then  appeared  as  a  closed  sac,  attached  by  a 
hollow  cord,  about  the  length  of  the  gland  itself,  to  the  base 
of  the  fang,  where  also  was  a  large  bundle  of  muscular 
fibre. 

FISH.— The  most  interesting  part  of  fish  to  the  micro- 
scopic anatomist  is  undoubtedly  the  breathing  apparatus. 


OF   MICROSCOPIC   OBJECTS.  169 

It  is  not  a  very  difficult  matter  to  open  the  head  and  remove 
the  gills,  which  are  very  beautiful.  Under  the  outer  covers 
lie  a  quantity  of  thin  plates  or  leaves  (as  of  a  book)  which 
in  different  fishes  are  of  various  shapes,  but  are  made  like 
net-work  by  the  numerous  veins  and  arteries  which  convey 
the  blood  to  be  acted  upon  by  the  air  and  gases  in  the 
water,  as  is  done  in  the  lungs  of  a  man.  These  plates  are 
of  such  numbers  that  in  a  good-sized  salmon  the  surface 
exposed  has  been  estimated  at  two  thousand  square  inches, 
i.e.,  about  fourteen  square  feet.  The  beauty  of  these  is, 
of  course,  not  perfectly  shown  until  they  are  injected,  which 
will  be  noticed  elsewhere. 

TONGUES,  OR  PALATES,  OF  MOLLUSCS. — Of  the  nature  of 
these,  Dr.  Carpenter  gives  the  following  description  : — "  The 
organ  which  is  commonly  known  under  this  designation  is 
one  of  a  very  singular  nature ;  and  we  should  be  altogether 
wrong  in  conceiving  of  it  as  having  any  likeness  to  that  on 
which  our  ordinary  ideas  of  such  an  organ  are  founded. 
For,  instead  of  being  a  projecting  body,  lying  in  the  cavity 
of  the  mouth,  it  is  a  tube  that  passes  backwards  and  down- 
wards beneath  the  mouth,  its  higher  end  being  closed, 
whilst  in  front  it  opens  obliquely  upon  the  floor  of  the 
mouth,  being,  as  it  were,  slit  up  and  spread  out  so  as  to 
form  a  nearly  flat  surface.  On  the  interior  of  the  tube,  as 
well  as  on  the  flat  expansion  of  it,  we  find  numerous  trans- 
verse rows  of  minute  teeth,  which  are  set  upon  flattened 
plates  ;  each  principal  tooth  sometimes  having  a  basal  plate 
of  its  own,  whilst  in  other  instances  one  plate  carries 
several  teeth."  These  palates,  or  tongues,  differ  much 
amongst  the  Gasteropods  in  form  and  size,  some  of  them 
being  comparatively  of  an  immense  length.  Many  are 
amongst  the  most  beautiful  objects  when  examined  with 
polarized  light.  They  must,  however,  be  procured  by  dis- 
section, which  is  usually  performed  as  follows  : — The  animal 
is  placed  on  the  cork  in  the  dissecting-trough  before  men- 
tioned, and  the  head  and  forepart  cut  open,  spread  out,  and 
firmly  pinned  down.  With  the  aid  of  fine  scissors  or  knife, 


170  PREPARATION   AND   MOUNTING 

the  tongue  must  be  then  detached  from  its  fastenings,  and 
placed  in  water  for  a  day  or  two,  when  all  foreign  matter  may 
with  a  little  care  be  removed.  In  what  way  it  should  be 
mounted  will  depend  on  the  purpose  for  which  it  is  intended. 
If  for  examination  as  an  ordinary  object,  it  may  be  laid 
upon  the  slide  and  allowed  to  dry,  which  arrangement  will 
show  the  teeth  very  well.  If  we  wish  to  see  it  as  it  is  natu- 
rally, it  must  be  mounted  in  a  cell  with  Goadby's  fluid  ;  but 
if  it  is  wanted  as  a  polarizing  object,  it  must  be  floated  upon 
a  slide,  allowed  to  dry  thoroughly,  and  then  Canada  balsam 
added  in  the  usual  manner. 

In  the  stomach,  also,  of  some  of  these  molluscs  teeth  are 
found,  which  are  very  interesting  objects  to  examine,  and 
must  be  dissected  out  in  the  same  manner  as  the 
tongues. 

Since  writing  the  above,  Dr.  Alcock  (whose  very  beau- 
tiful specimens  prove  him  to  be  a  great  authority  in  this 
branch)  has  published  some  of  his  experience  in  the  second 
volume  of  the  third  series  of  "  Memoirs  of  the  Literary  and 
Philosophical  Society  of  Manchester."  By  his  permission  I 
make  the  following  extract : — 

"This  closes  my  present  communication  on  the  tongues 
of  mollusca ;  but  as  some  members  may  possibly  feel 
inclined  to  enter  upon  the  inquiry  themselves,  I  think  it 
will  not  be  amiss  to  add  a  few  remarks  on  the  manner  in 
which  they  are  to  be  obtained. 

"  First,  as  to  the  kinds  best  worth  the  trouble  of  pre- 
paration. Whelks,  Limpets,  and  Trochuses  should  be  taken 
first.  Land  and  fresh-water  snails  can  scarcely  be  recom- 
mended, except  as  a  special  study, — their  tongues  being 
rather  more  difficult  to  find,  and  the  teeth  so  small  that 
they  require  a  high  power  to  show  them  properly.  It 
would  appear,  from  Spallanzani's  description  of  the  anatomy 
of  the  head  of  the  snail,  that  even  he  did  not  make  out  this 
part,  although,  in  his  curious  observations  on  the  reproduc- 
tion of  lost  parts,  he  must  have  carefully  dissected  more 
snails  than  any  other  man. 


or  MICROSCOPIC  OBJECTS.  171 

"  As  to  preserving  the  animals  till  wanted,  they  should 
simply  be  dropped  alive  into  glycerine  or  alcohol.  Glycerine 
is  perhaps  best  where  only  the  tongues  are  wanted  ;  but  it 
leaves  the  animals  very  soft;  and  as  it  does  not  harden 
their  mucus  at  all,  they  are  very  slippery  and  difficult  to 
work  upon  when  so  preserved. 

"  Then  as  to  the  apparatus  required  for  dissection.  In  the 
first  place,  all  the  work  is  to  be  done  under  water,  and  a 
common  saucer  is  generally  the  most  convenient  vessel 
to  use.  No  kind  of  fastening  down  or  pinning  out  of  the 
animal  is  needed ;  and,  in  fact,  it  is  much  better  to  have 
it  quite  free,  that  you  may  turn  it  about  any  way  you  wish. 
The  necessary  instruments  are  a  needle-point,  a  pair  of 
fine-pointed  scissors,  and  small  forceps  ;  the  forceps  should 
have  their  points  slightly  turned  in  towards  each  other. 

"  A  word  or  two  on  the  lingual  apparatus  generally,  and 
on  its  special  characters  in  a  few  different  animals,  will  con- 
clude what  I  have  to  say. 

"  The  mode  of  using  the  tongue  can  be  easily  seen  in  any 
of  the  common  water-snails,  when  they  are  crawling  on  the 
glass  sides  of  an  aquarium ;  it  may  then  be  observed  that 
from  between  the  fleshy  lips  a  thick  mass  is  protruded,  with 
a  motion  forwards  and  upwards,  and  afterwards  withdrawn, 
these  movements  being  almost  continually  repeated.  The 
action  has  the  appearance  of  licking;  but  when  the  light 
falls  suitably  on  the  protruded  structure,  it  is  seen  to  be 
armed  with  a  number  of  bright  points,  which  are  the  lingual 
teeth,  so  arranged  as  to  give  the  organ  the  character  and 
action  of  a  rasp. 

"If  you  proceed  to  dissection,  and  open  the  head  of  one 
of  these  mollusca  (say,  for  instance,  a  common  limpet),  you 
will  find  the  cavity  of  the  mouth  almost  filled  with  the  thick 
fleshy  mass,  the  front  of  which  is  protruded  in  the  act  of 
feeding ;  and  on  its  upper  surface,  extending  along  the 
middle  line  from  back  to  front,  is  seen  the  strong  membranous 
band  upon  which  the  teeth  are  set.  The  mass  itself  consists 
of  a  cartilaginous  frame,  surrounded  by  strong  muscles  ;  and 


172  PREPARATION  AND  MOUNTING 

these  structures  constitute  the  whole  of  the  active  part  of 
the  lingual  apparatus. 

"But  the  peculiarity  of  the  toothed  membrane,  which 
makes  its  name  of  ribbon  so  appropriate,  is,  that  there  is 
always  a  considerable  length  of  it  behind  the  mouth,  per- 
fectly formed,  and  ready  to  come  forward  and  supply  the 
place  of  that  at  the  front,  which  is  continually  wearing  away 
by  use. 

"  In  the  limpet  this  reserve  ribbon  is  of  great  length, 
being  nearly  twice  as  long  as  the  body,  and  the  whole  of  it 
is  exposed  to  view  on  simply  removing  the  foot  of  the  animal ; 
nothing,  then,  can  be  easier  than  to  extract  the  tongue  of 
the  common  limpet.  But,  unfortunately,  what  you  find  in 
one  kind  of  mollusc  is  not  at  all  what  you  find  in  another. 
In  the  Acmceas,  for  instance,  which  are  very  closely  related 
to  the  limpets,  and  have  shells  which  cannot  be  distinguished, 
the  reserve  portion  of  the  ribbon  has  to  be  dug  out  from  the 
substance  of  the  liver,  in  which  it  is  imbedded,  that  organ 
being,  as  it  were,  stitched  completely  through  by  a  long 

loop  of  it It  might  be  thought  a  comfortable 

reflection  that,  at  all  events,  one  end  of  the  ribbon  can 
always  be  found  in  the  mouth ;  but  in  many  cases  this  is 
about  the  worst  place  to  look  for  it.  Perhaps  it  may  appear 
strange  that  in  some  of  the  smaller  species,  with  a  retractile 
trunk,  a  beginner  may  very  likely  fail  altogether  in  his 
attempt  to  find  the  mouth  ;  if,  however,  the  skin  of  the  back 
be  removed,  commencing  just  behind  the  tentacles,  there  will 
be  very  little  difficulty  in  making  out  the  trunk,  which  either 
contains  the  whole  of  the  ribbon,  as  in  the  whelk,  or  the 
front  part  of  it,  as  in  Pnrpura  and  Murex,  where  a  free 

coil  is  also  seen  to  hang  from  its  hinder  extremity 

In  the  periwinkles  the  same  plan  of  proceeding,  by  at  once 
opening  the  back  of  the  animal,  is  best :  and  on  doing  so, 
the  long  ribbon,  coiled  up  like  a  watch-spring,  cannot  fail  to 
be  found. 

"  In  the  Trochuses,  and  indeed  in  all  the  Scutibrancliiaia, 
one  point  of  the  scissors  should  be  introduced  into  the 


OF  MICROSCOPIC   OBJECTS.  173 

mouth  of  the  animal,  and  an  incision  made  directly  back- 
wards in  the  middle  line  above  to  some  distance  behind  the 
tentacles ;  the  tongue  is  then  immediately  brought  into  view, 
lying  along  the  floor  of  the  mouth." 

Dr.  Alcock's  method  of  dissection  will  be  found  to  differ 
in  some  degree  from  the  general  rules  before  given ;  and 
when  the  tongue  is  dissected  out  he  washes  it  for  one  hour 
(shaking  it  now  and  then)  in  a  weak  solution  of  potash. 
After  cleaning  thoroughly  in  water,  it  must  be  mounted  by 
one  of  the  methods  before  mentioned. 

Mr.  Edwards,  of  New  York,  no  mean  authority,  gives  his 
experience  as  follows : — I  use  a  rather  strong  solution  of 
caustic  potassa,  the  strength  of  which  I  cannot  specify  as  it 
must  differ  with  the  species  under  manipulation,  as  somo 
ribbons  (or  tongues)  are  injured  much  sooner  than  others. 
Plunge  the  whole  animal  in  this  solution ;  in  the  case  of 
very  small  creatures  shell  and  all.  I  have  found  it  better 
to  let  the  animal  stand  until  it  dies  and  begins  to  decom- 
pose, when  it  can  readily  be  removed  and  falls  in  pieces. 
The  lingual  ribbon  is  not  so  easily  decomposed.  'Now  place 
and  leave  the  animal  in  the  potassa  solution  for  some  days, 
or  boil  at  once.  Almost  everything  is  now  dissolved  but 
the  shell,  some  few  fragments,  and  the  desired  ribbon. 
Wash  carefully  with  fresh  water,  and  if  it  is  to  be  preserved 
before  mounting,  remove  to  alcohol.  To  mount  it,  remove 
from  the  spirit  and  boil  a  short  time  in  turpentine,  when  it 
can  be  put  up  in  Canada  balsam.  Mr.  May  expresses  him- 
self as  "  standing  utterly  aghast "  at  any  man  so  interfering 
with  nature  as  to  put  up  these  objects  in  balsam,  thus 
pressing  and  destroying  their  true  forms.  He  recommends 
a  cell  and  a  weak  form  of  Goadby's  solution. 

Amongst  insects,  especially  the  grasshopper  tribe,  are 
found  many  which  possess  a  gizzard,  armed  with  strong 
teeth,  somewhat  similar  to  those  of  the  molluscs.  It 
requires  great  nicety  of  manipulation  to  obtain  these  for  the 
microscope;  but  Mr.  L.  G.  Mills,  before  quoted,  gives  the 
following  instructions  : — Kill  the  insect  with  chloroform  and 


174  PREPARATION   AND   MOUNTING 

place  it  in  a  vessel  of  water.  Hold  it  down  firmly  with  a 
pair  of  tweezers,  and  with  the  back  of  a  dissecting  knife 
draw  the  head  steadily  from  the  body.  The  head  brings 
with  it  the  stomach,  gizzard,  and  chief  portion  of  the  digestive 
tubes.  Place  all  these  under  a  dissecting  microscope,  when 
the  gizzard,  being  just  below  the  stomach  and  darker  in 
colour,  is  easily  distinguished,  and  may  be  separated  by  two 
cuts  with  the  knife.  It  then  forms  a  short  tube,  the  teeth 
being  inside.  The  opening-out  of  this  tube,  especially  if  it 
be  email,  requires  delicate  handling :  if  the  point  of  a  fine 
knife  can  be  fairly  inserted,  then  one  firm  cut  downward 
upon  the  glass  will  lay  open  the  gizzard.  Here  great  care 
is  needed ;  and  sometimes  it  is  well  to  put  a  fine  needle  up 
the  tube,  and  cut  down  upon  the  needle.  Among  the 
small  weevils  the  membrane  is  delicate,  so  that  great  care 
is  necessary. 

We  have  now  considered  most  of  those  objects  which 
require  any  peculiar  treatment  in  section-cutting,  &c. ;  but 
in  no  branch  of  microscopic  manipulation  is  experience  more 
necessary  than  in  this. 


OF   MICROSCOPIC    OBJECTS.  175 


CHAPTEE     VII. 

INJECTION. 

1.  INJECTION  is  the  filling  of  the  arteries,  veins,  or  other 
vessels  of  animals  with  some  coloured  substance,  in  order 
that  their  natural  arrangement  may  be  made  visible.  This 
is,  of  course,  a  delicate  operation,  and  needs  special  appa- 
ratus, which  I  will  now  attempt  to  describe. 

2.  Syringe. — This  is  usually  made  to  contain  about  two 
ounces.     On  each  side  of  the  part  next  to  the  handle  is  a 
ring,  so  that  a  finger  may  be  thrust  through  it,  and  the 
thumb   may  work  the   piston   as  in  an   ordinary  syringe. 
The  plug  of  the  piston  must  be  packed  with  soft  leather 
well  oiled  or  greased,  in  order  to  free  it  from  all  danger  of 
any  liquid  penetrating  it,  and  fit  so  closely  as  to  be  perfectly 
air-tight ;  and  if,  when  it  has  been  used  awhile,  it  is  found 
that  some  of  the  liquid  escapes  past  the  plug  into  the  back 
part  of  the  body,  it  must  be  repacked,  which  operation  will 
be  best  understood  by  examining  the  part.     These  syringes 
are  made  of  various  sizes,  but  in   ordinary  operations   the 
above  will  be  all  that  is  needed.     The  nozzle  is  about   an 
inch  long,  and  polished  so  accurately  that  there  is  no  escape 
when  fae  pipes  are  tightly  placed  upon  it  dry. 

3.  The  pipes  are   usually  about  an  inch   long,  to  their 
ends  are  affixed  thicker  tubes  so  as  to  n't  the  nozzle,   as 
before  mentioned,  whilst  a    short  arm  projects  from  each 
side  of  these,  so  that  the  silk  or  thread  which  is  used  to  tie 
the  artery  upon  the  thin  pipe,  may  be  carried  round  these 
arms,  and  all  danger  of  slipping  off  prevented.     The  pipes 
are  made  of  different  sizes,  from  that  which  will  admit  only 
of  a  very  fine  needle  (and  this  will  need  now  and  then  to  be 
cleaned,  or  to  be  freed  from  any  chance  obstruction),  to 


176  PREPARATION    AND    MOUNTING 

that  which  will  take  a  large  pin.  These  sizes  must  always 
be  at  hand,  as  the  vessels  of  some  subjects  are  exceedingly 
minute. 

4.  Stopcock. — This  is  a  short  pipe  like  a  small  straight 
tap,  which  fits  accurately  upon  the  end  of  the  syringe  like 
the  pipes,  and  also  takes  the  pipes  in  the   same  manner. 
The  use  of  this  is  absolutely  necessary  when  the  object  is 
so  large  that  one  syringe  full  of  liquid  will  not  fill  it.     If 
no  preventive  were  used,  some  part  of  the  liquid   would 
return  whilst  the  syringe  was  being  replenished,  but  the 
stopcock  is  then  turned  as  in   an   ordinary  tap,   and  all 
danger  of  this  effectually  removed. 

5.  Curved  needles. — These  are  easily  made  by  heating 
common  needles  at  the  end  where  the  eye  is  situated,  and 
bending  them  with  a  small  pair  of  pliers  into  a  segment  of 
a  circle  half  an  inch  in  diameter.     They  are,  perhaps,  more 
convenient  when  the  bent  part  is    thrown    slightly  back 
where  it  commences.     The  pointed  end  is  then  thrust  into 
a  common  penholder,  and  the  needle  needs  no  re-tempering, 
as  the  work  for  which  it  is  wanted  is  simply  to  convey  the 
thread  or  silk  under  any  artery  or  vessel  where  it  would  be 
impossible  to  reach  with  unassisted  fingers. 

6.  A  kind  of  forceps,  commonly  known  by  the  name  of 
"  bulldog  forceps,"  will  be  constantly  required  during  the 
process  of  injecting.     These  are  short,  usually  very  strong, 
but  not  heavy,  and  close  very  tightly  by  their  own  spring, 
which  may  be  easily  overcome  and  the  artery  so  released  by 
the  pressure  of  the  fingers.     When  any  vessel  has  not  been 
tied  by  the  operator,  and  he  finds  the  injected  fluid  escaping, 
one  of  these  "  bulldogs  "  may  be  taken  up  and  allowed  to 
close   upon  the  opening.     This  will  cause  very   little  in- 
terruption, and  the  stoppage  will  be  almost  as  effectual  as 
if  it  were  tied. 

7.  When  the  ordinary  mode  of  injection  is  employed,  it 
is  necessary  that  the  preparations  be  kept  warm  during  the 
time  they  are  used,  otherwise  the  gelatine  or  size  which  they 
contain  becomes  stiff,  and  will  not  allow  of  being  worked  by 


OF   MICROSCOPIC   OBJECTS.  177 

the  syringe.  For  this  purpose  we  must  procure  small 
earthenware  or  tin  pots  of  the  size  required,  which  will 
differ  according  to  the  kind  of  work  to  be  done ;  and  to  each 
of  these  a  loose  lid  should  be  adapted  to  protect  it  from 
dust,  &c.  These  pots  must  be  allowed  to  stand  in  a  tin 
bath  of  water,  under  which  a  lamp  or  gas  flame  may  be 
placed  to  keep  the  temperature  sufficiently  high  to  insure  the 
perfect  fluidity  of  the  mixture.  The  tin  bath  is,  perhaps, 
most  convenient  when  made  like  a  small  shallow  cistern ; 
but  some  close  it  on  the  top  to  place  the  pots  upon  it,  and 
alter  the  shape  to  their  own  convenience. 

8.  We  will  now  inquire  into  some  of  the  materials  which 
are  needed  in  this   operation  ;   the   first  of  which  is  size. 
This  substance  is  often  used  in  the  form  of  glue,  but  it  must 
be  of  the  very  best  and  most  transparent  kind.     To  make 
the  liquid  which  is  to  receive  the  colours  for  the  usual  mode 
of  injecting,  take  of  this  glue  seven  ounces,  and  pour  upon 
it  one  quart  of  clean  water ;  allow  this  to  stand  a  few 
hours,  and  then  boil  gently  until  it  is  thoroughly  dissolved, 
stirring  with  a  wooden  or  glass  rod  during  the  process. 
Take  all  impurities  from  the   surface,  and  strain   through 
flannel  or  other  fine    medium.      The  weather  affects  thi.^ 
a  little  as  to   its   stiffness  when  cold,  but  this    must  be 
counteracted  by   adding  a  little  more  glue  if  found   too 
liquid. 

9.  Instead  of  glue,  gelatine  is  generally  used,  especially 
when  the  work  to  be  accomplished  is  of  the  finer  kind.  The 
proportions  are  very  different  in   this  case,  one  ounce  of 
gelatine  to  about  fourteen  ounces  of  water  being  sufficient. 
This,  like  glue,  must  be  soaked  a  few  hours  in  a  small  part 
of  the  cold  water,  the  remainder  being  boiled  and  adder*, 
when  it  must  be  stirred  until  dissolved.     A  good  size  may 
be  made  by  boiling  clean   strips  of  parchment  for  awhile, 
and  then   straining  the  liquid  whilst  hot  through  flannel ; 
but  when  the  injections  are  to  be  transparent,  it  is  of  the 
greatest  importance  that  the  size  be  as  colourless  as  pos- 
sible.    For  this  nurpose  good  gelatine  must  be  employed, 


178  PREPABATION   A.ND   MOUNTING 

as  Nelson's  or  Cox's :  some  persons  of  experience  prefer  the 
latter. 

10.  Colours. — The    size-solution    above    mentioned   will 
need  some  colouring  matter  to  render  it  visible  when  in- 
jected into  the  vessels  of  an  animal,  and  different   colours 
are  used  when  two  or  more  kinds  of  vessels  are  so  treated, 
in   order   that   each    set   may   be   easily  distinguished   by 
sight.     The  proportion  in  which  these  colours  are  added  to 
the  size-solution  may  be  given  as  follows : — 

11.  For 

Red 8  parts  of  size-solution 

(by  weight)  to  1  part  of  vermilion. 

Yellow...  6         „  „  1       „       chrome  yellow. 

White  ...  5         „  „  1       „       flake-white. 

Blue  3         „  „  Is.       blue-smalt,  fine. 

Black  ...12         „  „  1       „       lampblack. 

Whichever  of  these  colours  is  used  must  be  levigated  in  a 
mortar  with  the  addition  of  a  very  small  quantity  of  water 
until  every  lump  of  colour  or  foreign  matter  is  reduced  to 
the  finest  state  possible,  otherwise  in  the  process  of  injecting 
it  will  most  likely  be  found  that  some  of  the  small  channels 
have  been  closed  and  the  progress  of  the  liquid  stopped. 
When  this  fineness  of  particles  is  attained,  warmth  sufficient 
to  render  the  size  quite  fluid  must  be  used,  and  the  colour 
added  gradually,  stirring  all  the  time  with,  a  rod.  It  may 
be  here  mentioned  that  where  one  colour  only  is  required, 
vermilion  is,  perhaps,  the  best ;  and  blue  is  seldom  used 
for  opaque  objects,  as  it  reflects  very  little  more  light  than 
black. 

12.  When  it  is  wished  to  fill  the  capillaries  (the  minute 
vessels  connecting  the  arteries  with  the  veins),  the  Micro- 
graphic  Dictionary  recommends  the  colouring  matter  to  bo 
made  by  double  decomposition.  As  a  professed  handbook 
would  be,  perhaps,  deemed  incomplete  without  some  direc- 
tions as  to  the  mode  of  getting  these  colours,  I  will  here 


OF  MICROSCOPIC  OBJECTS.  179 

use  those  given  in  that  work.  For  red,  however,  vermilion, 
as  above  stated,  may  be  used ;  but  it  must  be  carefully 
examined  by  reflected  light  to  see  whether  it  be  free  from 
all  colourless  crystals  or  not.  It  must  first  be  worked  in  a 
mortar,  and  then  the  whole  thrown  into  a  quantity  of  water 
and  stirred  about ;  after  leaving  it  not  longer  than  a  quarter 
of  a  minute,  the  larger  portions  will  settle  to  the  bottom, 
and  the  liquid  being  poured  off  will  contain  the  finer  powder. 
This  may  then  be  dried  slowly,  or  added  to  the  size  whilst 
wet  in  the  manner  before  advised. 

13.  Yellow  injection. — To  prepare  this,  take — 

Acetate  (sugar)  of  lead     380  grains. 

Bichromate  of  potash  152       „ 

Size 8  ounces. 

Dissolve  the  lead  salt  in  the  warm  size,  then  add  the  bichro- 
mate of  potash  finely  powdered. 

Some  of  the  chromic  acid  remains  free,  and  is  wasted  in 
this  solution,  so  the  following  is  given  : — 

Acetate  of  lead ....  190  grains. 

Chromate  of  potash  (neutral)  ...  100       ,, 
Size 4  ounces. 

The  first  of  these  has  the  deepest  colour,  and  is  the  most 
generally  used. 

14.  White  injection. — This  is  a  carbonate  of  lead  : — 

Acetate  of  lead     190  grains. 

Carbonate  of  potash 83      ,, 

Size 4  ounces. 

Dissolve  the  acetate  of  lead  in  the  warm  size,  and  filter 
through  flannel ;  dissolve  the  carbonate  of  potash  in  the 
smallest  quantity  of  water,  and  add  to  the  size:  143 
grains  of  carbonate  of  soda  may  be  substituted  for  the  car- 
bonate of  potash. 

N  2 


180  PREPARATION   AND  MOUNTING 

15.  For  blue  injection,  which  is  not,  however,  much  used 
with  reflected  light,  as  before  stated,  take — 

Prussian  blue 73  grains. 

Oxalic  acid 73      „ 

Size    4  ounces. 

The  oxalic  acid  is  first  finely  powdered  in  a  mortar,  the 
Prussian  blue  and  a  little  water  added,  and  the  whole  then 
thoroughly  mixed  with  the  size. 

16.  It  may  here  be  repeated,  that  it  is  only  when  the 
capillaries  are  to  be  filled  that  there  is  any  need  to  be  at  the 
trouble  to  prepare  the  colours  by  this  double  decomposition; 
and,  indeed,  colours  ground  so  finely  may  be  procured  that 
the  above  instructions  would  have  been  omitted,  had  it  not 
been  supposed  that  some  students  might  find  a  double  plea- 
sure in  performing  as  much  of  the  work  as  possible  by  their 
own  unaided  labours. 

17.  The  process  of  injection  may  now  be  considered ;  but 
it  is  impossible  for  written  instructions  to  supply  the  place 
of  experience.    I  will  do  my  best,  however,  to  set  the  novice 
at  least  in  the  right  way.     There  are  two  kinds  of  injection 
— one  where  the  object  and  colours  are  opaque,  and  conse- 
quently  fit  for   examination  by    reflected  light  only ;   the 
other,  where  the  vessels  are  filled  with  transparent  colours, 
and  must  be  viewed  by  transmitted  light.   The  first  of  these 
is  most  frequently  employed,  so  we  will  begin  with  it.     In 
the  object  which  is  to  be  injected,  a  vessel  of  the  kind  which 
we  wish  to  be  filled  must  be  found ;  an  opening  must  then 
be  made  in  it  to  allow  one  of  the  small  pipes  before  men- 
tioned to  be  thrust  some  distance  within  it.     When  this  is 
accomplished,  thread  the  curved  needle  with  a  piece  of  silk 
thread,  or  very  fine  string,  which  some  operators  rub  well 
with  beeswax.     This  thread  must  not  be  too  thin,  else  there 
is  danger  of  cutting  the  vessel.     The  cord  is  then  carried 
under  the  inserted  pipe,  and  the  vessel  bound  tightly  upon 
it,  the  ends  being  brought  up  round  the  transverse  arms, 


OF  MICROSCOPIC   OBJECTS.  181 

and  there  tied;  so  that  all  danger  of  accidentally  with- 
drawing the  pipe  is  obviated.  Care  must  now  be  used  in 
closing  all  the  vessels  which  communicate  with  that  where 
the  pipe  is  placed  lest  the  injecting  fluid  escape ;  and  this 
must  be  done  by  tying  them  with  silk.  Should,  however, 
any  of  these  be  left  open  by  accident,  the  bulldog  forceps 
must  be  used,  as  before  recommended. 

18.  The  part  to  be  injected  must  now  be  immersed  in 
warm  water,  not,  however,  above  100°  Fahrenheit,  and  left 
until  the  whole  is  thoroughly  warmed.  Whilst  this  is  being 
done,  the  coloured  size  must  be  made  ready  by  the  pot  being 
placed  in  the  tin  bath  of  warm  water,  which  must  be  of 
sufficient  temperature  (about  110°  Fahrenheit)  to  keep  it 
perfectly  liquid.  For  the  same  purpose,  the  syringe  is  often 
tightly  covered  with  two  or  three  folds  of  flannel;  and, 
indeed,  there  is  no  part  of  the  process  which  requires  more 
attention.  If  the  substance  to  be  injected  is  too  hot,  it  is 
injured ;  whilst,  if  any  of  the  articles  are  too  cold,  the  gela- 
tine, or  size,  loses  a  part  of  its  fluidity,  and  consequently 
cannot  enter  the  minute  vessels.  When  all  is  prepared,  the 
syringe,  with  the  stopcock  attached,  should  be  warmed,  and 
then  filled  and  emptied  with  the  injecting  fluid  two  or  three 
times,  care  being  taken  that  the  end  of  the  syringe  be  kept 
beneath  any  bubbles  which  form  upon  the  surface.  The 
syringe  may  then  be  filled,  and  closely  attached  to  the  pipe 
which  is  tied  in  the  vessel.  With  a  firm  and  steady  pressure 
the  piston  must  be  forced  downwards,  when  the  substance 
will  be  perceived  to  swell,  and  the  colour  show  itself  in  places 
where  the  covering  is  thin.  When  the  syringe  is  almost 
emptied  of  its  contents,  the  stopcock  must  be  turned  to  pre- 
vent any  escape  of  the  injection  from  the  subject.  It  must 
then  be  refilled,  as  in  the  first  instance,  and  the  process 
repeated.  I  say  almost  emptied,  because  it  is  well  not  to 
force  the  piston  of  the  syringe  quite  to  the  bottom,  lest  the 
small  quantity  of  air  which  frequently  remains  be  driven 
into  some  of  the  vessels,  and  the  object  be  injured  or  quite 
ruined.  As  the  injection  is  continued,  it  will  be  found  that 


182  PREPABATTON   AND   MOUNTING 

the  force  required  grows  greater,  yet  care  must  be  taken  not 
to  use  too  much,  or  the  vessels  will  burst,  and  render  all  the 
labour  fruitless.  The  movement  of  the  piston  must  be 
occasionally  so  slow  as  to  be  almost  imperceptible,  and  for 
this  reason  the  piston-rod  is  sometimes  marked  with  lines 
about  one- eighth  of  an  inch  apart. 

19.  Of  course,  during  the  whole  process  the  injecting 
fluid  and  subject  must  be  kept  at  a  temperature  high  enough 
to  allow  the  liquid  to  flow  freely  ;  and  the  escape  of  a  little 
of  it  need  cause  no  fears  to  the  operator,  as  it  is  almost  im- 
possible to  fill  a  subject  without  some  loss.  When  the 
injected  object  has  received  sufficient  fluid,  it  should  have  a 
plump  appearance,  owing  to  all  the  vessels  being  well  filled. 
The  vessel  must  then  be  tied  up  where  the  pipe  was  inserted, 
and  the  whole  left  in  cold  water  two  or  three  hours,  after 
which  time  it  may  be  mounted  ;  but  it  may  be  well  to  notice 
a  few  things  which  the  beginner  ought  to  know  before  enter- 
ing into  that  part  of  the  process;  and  he  may  be  here  informed 
that  it  is  not  necessary  to  mount  the  objects  immediately, 
otherwise  it  would  be  impossible  for  one  person  to  make 
use  of  half  of  any  large  subject,  as  it  would  be  in  a  state 
of  decay  long  before  each  part  could  have  been  examined 
and  separated.  Large  pieces  should  be  therefore  immersed 
in  equal  parts  of  spirits  of  wine  and  water,  or  glycerine, 
which  some  think  better  still,  and  thus  preserved  in  bottles 
until  time  can  be  given  to  a  closer  examination. 

2D.  In  operating  upon  large  subjects,  entire  animals,  &c., 
the  constant  pressure  required  by  the  piston  of  the  syringe 
grows  wearisome,  besides  occupying  both  hands,  which  is 
sometimes  inconvenient  when  working  without  assistance. 
To  obviate  this,  another  way  of  driving  the  syringe  was 
published  in  the  Micrographic  Dictionary  which  I  will 
quote  here: — ''We  have  therefore  contrived  a  very  simple 
piece  of  apparatus,  which  any  one  can  prepare  for  himself, 
p,nd  which  effects  the  object  by  mechanical  means.  It  con- 
teists  of  a  rectangular  piece  of  board,  two  feet  long  and  ten 
'inches  wide,  to  one  end  of  which  is  fastened  an  inclined 


OF   MICROSCOPIC   OBJECTS.  183' 

piece  of  wood  (equal  in  width  to  the  long  board,  and  one 
foot  high).  The  inclined  portion  is  pierced  with  three  holes, 
one  above  the  other,  into  either  of  which  the  syringe  may 
be  placed — the  uppermost  being  used  for  the  larger,  the 
lowermost  for  the"  smaller  syringe;  and  these  holes  are  of 
such  size  as  freely  to  admit  the  syringe  covered  with  flannel, 
but  not  to  allow  the  rings  to  pass  through  them.  The 
lower  part  of  the  syringe  is  supported  upon  a  semiannular 
piece  of  wood,  fastened  to  the  upper  end  of  an  upright  rod, 
which  slides  in  a  hollow  cylinder  fixed  at  its  base  to  a  small 
rectangular  piece  of  wood ;  and  by  means  of  a  horizontal 
wooden  screw,  the  rod  may  be  made  to  support  the  syringe 
at  any  height  required.  The  handle  of  the  syringe  is  let 
into  a  groove  in  a  stout  wooden  rod  connected  by  means  of 
two  catgut  strings  with  a  smaller  rod,  to  the  middle  of 
which  is  fastened  a  string  playing  over  a  pulley,  and  at  the 
end  of  which  is  a  hook  for  supporting  weights>  the  catgut 
strings  passing  through  a  longitudinal  slit  in  the  inclined 
piece  of  wood."  When  in  use  the  syringe  is  filled  with 
injecting  fluid,  and  passed  through  one  of  the  three  holes 
which  is  most  suitable.  The  object  being  placed  so  that  the 
pipe  and  syringe  can  be  best  joined,  the  rod  and  strings  are 
set  in  order,  and  a  weight  placed  on  the  hook.  The  stop- 
cock must  then  be  opened  gradually,  when  the  operator 
will  be  able  to  judge  whether  the  weight  is  a  proper  one  or 
not :  if  the  piston  is  driven  with  any  speed,  there  is  danger 
of  injuring  the  subject,  and  less  weight  may  be  used ;  if, 
however,  the  piston  do  not  move,  more  must  be  added.* 

21.  Such  is  the  method  recommended  in  the  Micro- 
graphic  Dictionary,  and  perhaps  it  is  as  good  as  any 
mechanical  plan  could  be  ;  but  where  the  operator  is  willing 
to  undergo  the  labour  of  performing  all  this  with  the  hand, 
he  has  a  much  better  chance  of  succeeding,  because  the 
pressure  can  be  regulated  so  accurately,  and  changed  so 

*  There  is  in  the  Monthly  Microscopic  Journal,  vol.  ii.,  page  48, 
another  ingenious  apparatus  for  injecting  purposes. 


184  PREPARATION   AND   MOUNTING 

quickly  when  requisite,  that  no  mere  machine  can  compete 
with  it,  however  well  contrived. 

22.  When  the  beginner  attempts  to  inject  a  subject,  one 
of  his  difficulties  is  finding  the  vessel  from  which  to  com- 
mence.     Another  consists    in    distinguishing    the    arteries 
from  the  veins ;  but  this  is  partly  removed  by   making  a 
longitudinal  incision  in  the  vessel,  and  with  a  blunt  thick 
needle  probing  a  little  distance  into  the  tube.     The  artery 
will  be  found  thicker  in  the  coating  than  the  vein,  and  the 
difference  is  easily  perceived  by  this  mode  of  testing :  the 
vein  is  also  of  a  bluer  colour  than  the  artery.     I  say  above, 
a  "  longitudinal  incision  "  must  be  made  :  the  reason  for  this 
is,  that  an  artery  when  cut  across  contracts  considerably,  and 
is  lost  in  the  adjoining  substance ;  but  where  the  opening 
is  made  longitudinally   all   danger  of   this  contraction    is 
obviated. 

23.  The  different  systems  of  vessels  are  often   injected 
with    various    colours,    so    that    their    relative    positions, 
may  be  shown  more  clearly.     In  some  specimens,  the  veins 
are  injected  with  white,  and  the  arteries  with  red ;  in  the 
kidney,  the  urinary  tubes  are  often   filled  with  white,  and 
the  arteries  with  red.     Then,  again,  the  liver  affords  tubes 
for  three  or  four  colours.     But  no  written  instructions  on 
this  point  can  benefit  the  young  student,  and  he  must  be 
content  for  a  while  to  employ  himself  with  single  colours 
until  he  has  gained  the  mechanical  skill  and  the  primary 
knowledge  which  are   necessary  before  he  can   make  any 
advance. 

24.  We  will  now  consider  the  best  methods  of  mounting 
injected   objects.      They   must  always  be   well  washed   in 
water  after  they  have  been  kept  in  any  preservative  liquid, 
using  a  camel-hair  pencil  to  clean  the  surface  if  necessary. 
Many  parts  when  injected  are  in  masses,  such  as  the  lungs, 
liver,  &c.,  of  animals,   and  consequently   sections   of  these 
must  be  cut.      For  this  purpose  Valentin's   knife  is   very 
convenient,  as  the  thickness  can  be  regulated  so  easily ;  but 
where  the  injections  are  opaque,  there  is  no  need  to  have  the 


OF   MICBOSCOPIC   OBJECTS.  185 

sections  very  thin.  Some  few  of  this  kind  undergo  compara- 
tively little  change  in  drying,  so  that  the  section  may  be 
well  washed  and  floated  upon  the  glass  slide  in  the  place 
desired,  where  it  will  dry  perfectly  and  adhere  to  it.  It 
must  then  be  moistened  with  turpentine  and  mounted  in 
Canada  balsam  like  other  objects.  No  great  heat  should  be 
used  with  these  preparations,  as  it  is  very  liable  to  injure 
them ;  and  some  of  the  colours  seem  to  suffer  a  slight  con- 
traction when  any  great  degree  of  warmth  is  applied.  There 
are  many  objects,  however,  which  must  be  seen  in  the  mass 
to  be  understood,  and,  indeed,  lose  all  their  form  and  beauty 
in  drying,  such  as  certain  parts  of  the  intestines,  &c.  These 
must  be  mounted  in  fluid,  with  the  precautions  noticed  at 
length  in  Chapter  V.,  and  for  this  purpose  either  Goadby's 
fluid,  the  chloride  of  zinc  solution,  or  spirit  diluted  with  ten 
parts  of  distilled  water,  may  be  employed.  It  is  a  good 
thing,  when  practicable,  to  mount  similar  objects  on  two 
separate  slides,  using  different  preservative  liquids,  and 
taking  the  precaution  of  marking  each  with  the  kind  of 
liquid  employed.  This  not  only  serves  as  a  guide  to  what  is 
best  for  certain  subjects,  but  if  one  is  injured,  there  will 
probably  be  a  good  specimen  in  the  other. 

25.  It  may  be  here  mentioned  that  many  are  now  mount- 
ing  sections  of  injected   substances  with  the  balsam  and 
chloroform  before  mentioned,  instead  of  using  balsam  alone, 
and  consider  that  the  labour  is  much  lessened  thereby. 

26.  A  description  of  that  mode  of  injection  which  is  most 
generally  employed  has  now  been  given,  but  this  is  not  the 
only  method  of  effecting  our   object.     A   most   ingenious 
process  was  invented  by  M.  Doyers,  requiring  no  artificial 
warmth,  by  which  many  beautiful  objects  have  been    pre- 
pared.   Make  a  solution  of  bichromate  .of  potash,  524  grains 
to  a  pint  of  water,  and  throw  this  into  the  vessels  to  be 
injected;  then  take  1,000  grains  of  acetate  of  lead  dissolved 
in  half  a  pint  of  water,  and  force  this  into  the  same  vessels. 
A  decomposition  now  takes  place  in  the  vessels,  and  the 
yellow  chromate  of  lead  is  formed.     In  this  decomposition, 


186  PKEPAKATION   AND   MOUNTING 

however,  the  acetate  of  potash  also  is  formed  and  as  this 
salt  has  an  injurious  action  upon  the  cells,  Dr.  Goadby 
recommends  nitrate  of  lead  to  be  used,  which  preserves 
rather  than  destroys  them.  He  also  advises  the  addition 
of  two  ounces  of  gelatine  dissolved  in  eight  ounces  of  water, 
to  eight  ounces  of  the  saturated  solution  of  each  salt ;  but 
with  this  addition  the  hot-water  bath  would  be  required  to 
keep  the  injecting  fluid  liquid. 

27.  Many  of  these  are  best  mounted  in  balsam,  in  the 
same  manner  as  those  made  in  the  ordinary  way ;  whilst 
others  are  best  shown  when  preserved  in  liquids,  for  which 
purpose  Goadby's  fluid  may  be  employed. 

28.  This  mode  of  making  injections  with  chromate  of  lead 
is  deemed  by  many  the  best,  especially  where  one  colour 
only  is  employed.     But  it  must  be  allowed  that  there  is  a 
little  more  danger  of  failure  where  two  separate  fluids  are 
used  for  the  same  vessels. 

29.  We  will  now  consider  the  best  manner  of  making 
transparent  injections,  which,  for  many  purposes,  possess  an 
undoubted  advantage  over  opaque  ones.     But  it  must  be 
remembered  that  there  are  certain   subjects   to  which   no 
transparent  injection  could  be  applied,  as  they  are  too  thick 
when  in  their  natural  state,  and  cutting  would  destroy  all 
that  beauty  which  is  shown  by  the  different  parts  in  their 
relative   adaptation.      For   those   objects,  however,  which 
must  be  cat  into  sections  to  display  their  wonders,  or  are 
naturally  thin — such  as  some  of  the  finer  tissues,  livers, 
kidneys,    &c., — transparency    is    a    great    acquisition,   and 
enables  us  to  understand  the  arrangement  of  the  vessels 
more  perfectly.     Again,  another  advantage  is  the  simplicity 
of  the  process ;  no  hot   water  is  needed   with  some  pre- 
parations, either  for  the  subject  or  the  injecting  fluid,  which 
runs  into  the  minute  vessels  thoroughly  and  easily,  whilst 
the  cost  is  small. 

30.  For  this  kind  of  injection  no  colour  is    so  commonly 
•used  as  Prussian  blue.     It  is  not  a  good  one,  as  was  before 
stated,  for  any  opaque  object,  the  light  reflected  from  it 


OP   MICKOSCOPIC   OBJECTS.  187 

appearing  almost  black ;  yet  by  transmitted  light  no  colour 
is  more  useful,  because  its  distinctness  is  equally  great  by 
artificial  light  and  ordinary  daylight.  The  method  of  pre- 
paring this,  as  given  by  Dr.  Beale,  is  as  follows  :  — 

Glycerine  1  ounce. 

Wood  naphtha,  or  pyroacetic  acid    1|  drachm. 

Spirits  of  wine 1  ounce. 

Ferrocyanide  (yellow  prussiate)  of  potas- 
sium    12  grains. 

Tincture  of  sesquichloride  of  iron 1  drachm. 

Water    4  ounces. 

Dissolve  the  ferrocyanide  of  potassium  in  one  ounce  of  the 
water ;  add  the  tincture  of  sesquichloride  of  iron  to  another 
ounce.  Mix  these  solutions  gradually  together,  shaking  the 
bottle  well  which  contains  them — it  is  best  to  add  the  iron 
to  the  potash  solution.  When  thoroughly  mixed,  these 
solutions  should  produce  a  dark-blue  mixture,  perfectly 
free  from  any  perceptible  masses  or  flocculi.  Next  mix  the 
naphtha  and  spirits  of  wine,  and  add  the  glycerine  and  the 
remaining  two  ounces  of  water.  This  must  now  be  slowly 
mixed  with  the  blue  liquid,  shaking  the  whole  well  in  a 
large  bottle  whilst  the  two  come  together.  The  tincture  of 
sesquichloride  of  iron  is  recommended,  because  it  can  always 
be  obtained  of  a  uniform  strength. 

31.  Dr.  Turnbull  used  a  mixture  slightly  different  from 
the  above,  which  is  made  with  the  sulphate  of  iron  : — 

Purified  sulphate  of  iron     10  grains. 

Ferrocyanide  of  potassium  32  grains. 

Glycerine     1  ounce. 

Pyroacetic  acid    1|  drachm. 

Alcohol 1  ounce. 

Water 4  ounces. 

Dissolve  the  sulphate  of  iron  in  one  ounce  of  the  water, 


188  PREPARATION   AND   MOUNTING 

gradually  add  the  ferrocyanide  of  potassium  dissolved  in 
another  ounce,  and  proceed  as  before. 

32.  Dr.  Beale  also  gives  us  the  following  carmine  injection 
to  be  employed  in  the  same  way  as  the  blue.*     Take — 

Carmine 5  grains. 

Glycerine,  with  8  or  10  drops  of  hydro- 
chloric acid     -|  ounce. 

Glycerine  (pure)     1  ounce. 

Alcohol 2  drachms. 

Water    6  drachms. 

Mix  the  carmine  with  a  few  drops  of  water,  and  when  well 
incorporated  add  about  five  drops  of  liquor  ammonise.  To 
this  dark-red  solution  about  half  an  ounce  of  the  glycerine 
is  to  be  added,  and  the  whole  well  shaken  in  a  bottle. 
Next,  very  gradually  pour  in  the  acid  glycerine,  frequently 
shaking  the  bottle  during  admixture.  Test  the  mixture 
with  blue  litmus-paper,  and  if  not  of  a  very  decidedly  acid 
reaction,  a  few  more  drops  of  acid  may  be  added  to  the 
remainder  of  the  glycerine  and  mixed  as  before.  Lastly, 
mix  the  alcohol  and  water  very  gradually,  shaking  the  bottle 
thoroughly  after  adding  each  successive  portion  till  the 
whole  is  mixed.  This  fluid  may  be  kept  ready  prepared, 
and  injections  made  very  rapidly  with  it. 

33.  The  method  of  making  injections  with  these  colours 
is  the  same  as  with  the  gelatine  mixtures  before  described, 
except  that  no  heat  is  required,  and  consequently  most  of 
the  trouble  removed.     The  bottle  of  the  fluid  must  be  well 
shaken  immediately  before  use ;    and  when  the  object  has 
been  injected,  we  must  allow  it  to  remain  in  a  cool  place  for 
a  few  hours  before  cutting  it.     Thin  sections  of  the  subject 
may  be  cut  with  Valentin's  knife,  as  before   described,  and 

*  When,  however,  it  is  desirable  to  cut  very  thin  sections  of  the 
injected  subject,  the  carmine  is  sometimes  added  to  a  solution  of  fine 
gelatine — gelatine  one  part  to  water  eight  parts.  But  the  warm  water 
and  mode  of  proceeding  which  are  used  with  the  size  solutions  before 
described  will  be  necessary  in  this  case  also. 


OP  MICKOSCOPIC   OBJECTS.  189 

Are  very  beautiful  transparent  objects.  Some  of  the  finer 
tissues,  also,  are  shown  much  better  by  this  mode  of  in- 
jection than  by  the  opaque,  and  are  easily  mounted  by 
washing  in  clean  water  when  first  separated,  and  floating 
upon  a  slide,  where  they  must  be  allowed  to  dry  thoroughly. 
They  may  then  be  immediately  mounted  in  balsam,  or  kept 
in  the  dry  state  until  it  is  convenient  to  finish  them ;  but 
in  many  cases  this  keeping,  if  too  much  prolonged,  will 
injure  the  object.  If  it  is  desired  to  transfer  the  section  to 
another  slide,  it  will  be  necessary  to  wet  it  thoroughly  with 
water  by  the  aid  of  a  camel-hair  pencil,  and  then  gently 
strip  it  off  with  the  forceps.  When  it  is  wished  to  preserve 
injected  subjects  in  masses,  it  must  be  done  by  immersioii 
in  spirit,  and  the  sections  may  be  cut  at  leisure.  Most  of 
these  transparent  objects  may  be  mounted  in  Canada 
balsam ;  but  some  recommend  glycerine  or  glycerine  jelly, 
as  allowing  the  use  of  a  higher  power  in  their  examination, 
and  preserving  them  in  a  more  natural  form. 

34.  A  few  subjects  may  be  noticed  .which  are  very  beauti- 
ful when  injected,  and  amongst  these  are  the  eyes  of  many 
animals.  They  must  be  injected  by  the  artery  in  the  back 
part,  and  when  the  blue  transparent  liquid  is  employed, 
nothing  can  exceed  the  delicate  beauty  displayed  by  some 
of  the  membrane.  It  must  be  dissected  with  care,  but  well 
repays  us  for  the  trouble.  Water-newts  and  frogs  are  not 
difficult  subjects,  and  in  their  skin  and  other  parts  are  many 
interesting  objects.  Amongst  the  commoner  animals — rats, 
rabbits,  cats,  &c. — almost  endless  employment  may  be 
found,  making  use  either  of  portions  or  the  whole  animal  at 
once.  The  intestines  of  many  of  these  are  very  beautiful. 
We  must  divide  them  with  a  pair  of  scissors  along  the  tube, 
and  cleanse  them  from  the  contents ;  the  specimen  may 
then  be  laid  upon  a  slide,  and  any  remaining  impurity 
removed  by  a  camel-hair  pencil  and  water.  When  dried  it 
may  be  mounted  in  balsam,  and  having  been  injected  with 
the  transparent  blue,  its  minute  beauty  is  shown  most  per- 
fectly. In  injecting  a  sheep's  foot,  which  is  a  good  object, 


190  PREPARATION   AND   MOUNTING 

the  liquid  should  be  forced  into  it  until  a  slight  paring  of 
the  hoof  shows  the  colour  in  the  fine  channels  there. 
Perhaps  one  of  the  most  beautiful  and  interesting  objects  is 
the  skin  or  section  of  a  cat's  tongue.  On  examination  we 
shall  readily  learn  the  reason  why  we  feel  such  a  roughness 
when  we  allow  the  cat  to  apply  her  tongue  to  our  hands. 
In  appearance  we  shall  be  almost  ready  to  say  that  there  is 
no  little  resemblance  in  the  arrangement  betwixt  this  tongue 
and  those  of  the  molluscs  already  described.  The  liver  of  a 
rabbit  or  any  other  animal  is  an  easy  and  beautiful  object 
for  injection.  Sections  made  with  Valentin's  knife,  and 
mounted  in  balsam,  are  not  at  all  difficult,  and  worth  double 
the  time  they  occupy. 

35.  "When  the  lungs  of  small  animals  are  injected,  the 
finest  fluid  must  be  used,  as  some  of  the  capillaries  are  so 
small  that  it  is  not  an  easy  matter  to  fill  them  properly. 
And  before   entering  upon   these   subjects,   a   certain  pro- 
ficiency in  the  mode  of  using  the   syringe,  &c.,  should  be 
obtained  by  practising  upon  simpler  parts. 

36.  No  subjects  are   more  difficult   to  inject  than  fish, 
owing  to  the  extreme  softness  of  their  tissues.     Mr.  Hogg 
recommends  the  tail  of  the  fish  to  be  cut  off,  and  the  pipe 
to  be  put  into  the  divided  vessel  which  lies  just  beneath  the 
spinal  column ;  by  which  method  beautiful  injections  may 
be  made.     The  gills,  however,  are  the  most  interesting  part 
as  microscopic  objects. 

37.  These  instructions  may  seem  very  imperfect  to  those 
who  have  had  much   experience  in  this  branch  ;  but  they 
will  remember  that  their  own  knowledge  was  not  gained 
from  any  written   descriptions,  but  was  forced  upon  them 
by  frequent  failures,  some  of  which  probably  were  very  dis- 
heartening.    As  I  before  stated,  it  is  very  difficult  (if  not 
impossible)  to  accomplish  much  without  some  knowledge  of 
anatomy. 

38.  I  may  here  mention  that  the  transparent  injections 
sent  over  from  the  Continent  are  beautifully  executed  by 
Hyrtl  of  Vienna  (who  states  that  the  injected  fluid  ia  com- 


OF   MICROSCOPIC   OBJECTS.  191 

posed  of  gelatine  and  carmine),  Dr.  Oschatz  of  Berlin, 
the  Microscopic  Institute  of  Wabern,  Schaffer  and  Co.  of 
Magdeburg,  and  others.  Some  of  these  will  bear  examining 
with  a  high  power.  A  friend  informs  me  that  he  measured 
a  vessel  in  a  rat's  tongue  by  Hyrtl,  which  was  l-7200th 
of  an  inch  in  diameter,  and  had  a  clear  outline  with  quarter- 
inch  objective.  He  has  also  made  many  experiments  with 
the  same  materials,  but  has  as  yet  failed  in  producing 
perfectly  distinct  outline?,  there  being  a  tendency  of  the 
colouring  matter  (magenta,  carmine,  &c.)  to  diffuse  itself 
through  the  coats  of  the  vessels  into  the  surrounding  tissues, 
although  he  has  varied  the  pressure  from  half  a  pound  to 
sixty  pounds.  He  believes  the  vessels  are  first  washed  out 
(injected  with  warm  water  and  pressure  applied),  then  some 
fluid  introduced,  probably  solution  of  tannin,  which  renders 
the  arteries  impervious  to  the  coloured  fluid  afterwards  in- 
jected. 

39.  He  finds  that  after  washing  out  the  vessels  as  above, 
the  injecting  fluid  is  much  more  easily  introduced.  He  has 
used  a  strong  solution  of  gallic  acid  previously  to  injecting 
with  the  colouring  matter  (in  one  experiment  only),  and  the 
result  was  satisfactory.  He  puts  the  query, — Might  not 
carbolic  acid  have  a  similar  effect  ?  He  has  often  used  it 
with  injections  to  preserve  the  specimens,  but  not  in  suf- 
ficient quantity  to  act  in  the  way  indicated  above. 

Since  writing  the  above,  Mr.  J.  G.  Dale,  F.O.S.,  and  I 
have  made  numerous  experiments  with  carmine  injection, 
and  have  at  length  been  favoured  with  what  we  deem 
success.  Some  of  the  vessels  in  a  kitten  lately  injected  do 
not  exceed  1 -2000th  of  an  inch  in  diameter,  and  present  a 
clear  outline  with  one-fifth  objective.  There  is  no  extra- 
vasation, neither  does  the  colouring  matter  show  any  grain 
except  when  a  very  high  power  is  employed.  The  following 
is  our  process  : — 


192  PREPARATION   AND   MOUNTING 

Take  180  grains  best  carmine. 

|  fluid  ounce  of  ammonia,  commercial  strength, 

viz.,  0'92,  or  15°  ammonia  meter. 
3  or  4  ounces  distilled  water. 

Put  these  into  a  small  flask,  and  allow  them  to  digest  with- 
out heat  from  twenty-four  to  thirty-six  hours,  or  until  the 
carmine  is  dissolved.  Then  take  a  Winchester  quart  bottle, 
and  with  a  diamond  mark  the  spot  to  which  sixteen  ounces 
of  water  extend.  The  coloured  solution  must  be  filtered 
into  the  bottle,  and  to  this  pure  water  should  be  added 
until  the  whole  is  equal  to  sixteen  ounces. 

Dissolve  600  grains  potash  alum  in  ten  fluid  ounces  of 
water,  and  add  to  this,  under  constant  boiling,  a  solution  of 
carbonate  of  soda  until  a  slight  permanent  precipitate  is 
produced.  Filter  and  add  water  up  to  sixteen  ounces.  Boil 
and  add  the  solution  to  the  cold  ammoniacal  solution  of 
carmine  in  the  Winchester  quart,  and  shake  vigorously  for 
a  few  minutes.  A  drop  of  this  placed  upon  white  filtering- 
paper  should  show  no  coloured  ring.  If  much  colour  is  in 
solution  the  whole  must  be  rejected,  because,  although 
it  is  possible  to  precipitate  all  the  colouring  matter  by 
the  addition  of  ammonia  or  alum,  it  is  not  well  to  do 
so,  as  the  physical  condition  of  the  precipitate  is  thereby 
altered. 

Supposing  the  precipitation  to  be  complete,  or  very 
nearly  so,  shake  vigorously  for  at  least  half  an  hour,  and 
allow  it  to  stand  until  quite  cold.  The  shaking  must  then 
be  renewed  for  some  time,  and  the  bottle  filled  up  with  pure 
water. 

After  allowing  the  precipitate  to  settle  a  day,  draw  off 
the  clear  supernatant  fluid  with  a  syphon.  Kepeat  the 
washing  until  the  clear  liquid  gives  little  or  no  precipitate 
with  chloride  of  barium.  So  much  water  must  be  left 
with  the  colour  at  last  that  it  shall  measure  forty  fluid 
ounces. 


OF    MICROSCOPIC    OBJECTS.  193 

For  the  injecting  fluid,  take  24  onnces  of  the  coloured 
liquid  thus  prepared,  and  three  ounces  of  good  gelatine. 
Allow  these  to  remain  together  twelve  hours,  and  then 
dissolve  by  the  heat  of  a  water-bath ;  after  which  it  should 
be  strained  through  fine  muslin. 

As  this  injecting  fluid  contains  gelatine,  the  hot  water, 
and  other  contrivances  mentioned  in  a  former  part  of  the 
chapter,  will  be  necessary  here  also,  but  no  peculiar  treat- 
ment will  be  required. 

Since  writing  the  above  concerning  carmine  injection,  I 
have  had  the  misfortune  to  lose  my  friend  Mr.  Dale,  but  not 
before  we  made  scores  of  experiments  together,  with  this 
formula.  Our  experience,  I  may  say  without  vanity,  justi- 
fies me  in  declaring  that  a  good  operator  can  get  results 
equal  to  any  that  he  will  receive  from  the  Continent,  as  far  as 
colour  and  distinctness  are  concerned.  The  colour,  being 
thoroughly  precipitated,  cannot  stain  the  tissues,  and  the 
course  is  thus  clear  and  well  defined.  If  the  object  is  small, 
it  is  well  to  use  the  mixture  with  25  or  30  ounces  of  water 
instead  of  40 ;  but,  with  this  exception,  I  know  of  nothing 
that  needs  alteration.  I  have,  time  after  time,  measured 
vessels  thoroughly  filled  with  good  colour  —  especially 
amongst  fatty  portions, — and  found  them  betwixt  l-3000th 
and  l-4000th  of  an  inch.  As  some  young  students  might 
say  "  Give  me  an  account  of  something  done  with  it,"  I  will 
endeavour  to  describe  my  use  of  part  of  a  horse's  leg.  My 
friend  Mr.  Hepworth  wrote  to  me  that  he  had  a  horse's  leg, 
and  should  be  glad  if  I  would  come  over  with  sufficient  car- 
mine to  inject  it.  I  took  three  pints  of  solution,  and  may 
here  mention  that,  with  a  very  slight  loss  indeed,  all  this 
liquid  was  thrown  into  our  subject.  The  leg  was  cut  off 
just  beneath  the  knee,  and  before  using  it  we  allowed  it  to 
remain  in  water  about  80°  or  90°  Fahrenheit  two  or  three 
hours,  and  then  introduced  our  syringe  into  an  artery  at 
the  top.  As  I  have  no  faith  in  any  mechanical  contrivance, 

o 


194  PREPARATION   AND   MOUNTING 

I  need  the  common  syringe,  and  filled  the  leg  with  the 
liquid.  We  then  placed  it  in  cold  water,  and  allowed  it  to 
remain  until  the  next  morning. 

The  first  work  was  to  remove  a  piece  of  the  skin,  and 
take  sections  of  it  by  the  aid  of  a  "Valentin's  knife.  The 
arteries  were  shown  beautifully ;  but  the  most  attractive 
part  was  where  the  growth  of  the  hair  was  laid  open  before 
us.  Eacji  hair  exactly  resembled  a  common  onion,  whilst 
every  bulb  was  surrounded  by  a  perfect  network  of  arteries ; 
and  where  any  bulb  had  been  torn  out  by  accident,  there 
was  left  a  minute  bird's-nest  of  them,  clearly  showing  how 
they  had  been  intertwined  around  some  lost  friend.  Dif- 
ferent sections  of  the  muscular  portions  showed  every  phase 
of  arterial  distribution,  with  some  exquisitely  minute  vessels 
in  parts.  I  then  took  an  artery  and  cut  cross  sections,  in 
which  the  carmine  portions  were  as  closely  interwoven  as 
wickerwork.  I  also,  with  a  pair  of  scissors,  laid  open  a 
length  of  the  artery,  and  mounted  it,  together  with  a  cross 
section.  In  the  same  way  I  used  the  veins.  Many  of  the 
nerves  we  took  out,  and,  after  cleaning  carefully  with  knives 
and  small  brushes  where  necessary,  mounted  them  with 
the  attend  ant  arteries  around  them.  But  as  we  approached 
the  hoof,  double  interest  was  given  us.  The  skin  with  its  hairs 
just  above  the  hoof  plainly  showed  the  change  taking  place, 
and  sections  of  the  hoof  gave  beautiful  specimens  of  where 
circulation  was  gradually  stayed  by  the  growth  of  harder 
substance.  Here,  too,  we  reached  the  laminas,  or  thin 
plates  (somewhat  resembling  the  gills  of  certain  fishes), 
the  exact  use  of  which,  we  have  no  space  to  discuss — and 
these  were  readily  removed  by  the  aid  of  scissors  and 
knife.  In  these  the  vessels  are  minutely  and  exquisitely 
shown. 

These  are  a  few  of  the  beauties  which  this  injection 
afforded  me.  My  friend  Mr.  Hepworth  and  I  worked  to- 
gether at  this  subject  for  a  week  or  two,  and  part  of  the 
knowledge  which  he  gained  from  it  was  communicated  to 


OF   MICROSCOPIC   OBJECTS.  195 

the  microscopic  world  in  the  fifth  volume  of  their  Journal, 
where  the  illustrations  are  beautifully  printed.  "We  took 
about  1,000  slides  from  this  leg,  but  could  easily  have  taken 
a  specimen  for  every  microscopist  in  the  country.  What 
few  slides  I  now  have  are  mostly  mounted  in  balsam,  and 
are  quite  aa  good  in  colour  and  every  way  as  beautiful  as 
on  the  day  they  were  mounted. 


o  2 


196  PREPARATION   AND   MOUNTING 


CHAPTEE     VIII. 

MISCELLANEOUS. 

IT  must  be  evident  to  all  readers  that  there  are  various 
objects  of  interest  to  the  microscopist  which  cannot  be 
properly  placed  amongst  any  of  the  forementioned  classes, 
Imt  must  not  be  omitted  in  such  a  guide  as  this  professes 
to  be.  Of  these  may  be  mentioned  the  circulation  of  the. 
blood  in  various  animals,  the  rotary  motion  of  the  fluid 
in  many  plants,  the  best  means  of  taking  minute  pho- 
tographs, &c.  &c. 

Perhaps  the  most  interesting  of  these  objects  is  the  circu- 
lation of  the  blood  through  the  finer  vessels  of  various  parts 
of  animals  used  for  these  purposes,  which  parts,  it  is  evident, 
must  be  very  transparent  to  afford  a  perfect  view  of  this 
phenomenon.  The  web  of  the  frog's  foot  is  very  frequently 
employed,  but  requires  a  certain  arrangement,  which  we  will 
now  describe.  A  piece  of  thin  wood  (Dr.  Carpenter  recom- 
mends cork)  is  taken,  about  eight  inches  long  and  three 
wide ;  about  an  inch  from  one  end  is  cut  a  hole,  half  or 
three-quarters  of  an  inch  in  diameter.  The  body  of  the 
frog  is  then  placed  in  a  wet  bag,  or  wrapped  in  wet  calico, 
whilst  the  hind  foot  projects  ;  the  whole  is  then  laid  upon 
the  piece  of  wood,  so  that  the  foot,  which  is  left  free,  may  be 
extended  over  the  hole.  The  web  must  then  be  spread  out, 
and  secured,  either  by  loops  of  thread  fastened  to  the  toes 
and  attached  to  small  pins  placed  around  the  hole  in  the  wood, 
or  the  pins  may  be  inserted  into  the  wood — through  the 
web.  A  few  bands  of  tape  must  be  passed  round  the 
body,  the  leg,  and  thfi  wood,  to  prevent  any  disarrangement 
arising  from  the  struggles  of  the  animal.  Care  must  be 


OF   MICROSCOPIC   OBJECTS.  197 

taken  that  the  tape  be  not  too  tight,  else  the  circulation  will 
be  very  slow  or  altogether  stopped.  The  wood  must  now  be 
fixed  upon  the  stage,  with  the  aperture  under  the  object- 
glass  :  this  is  sometimes  done  by  simply  binding  it,  or  a 
spring  is  fixed  so  as  to  accomplish  the  same  object  without 
so  much  trouble.  With  a  half-inch  power  the  blood  may 
be  seen  to  flow  very  distinctly.  The  frog  may  be  used  for 
hours  if  care  be  taken  to  prevent  the  web  from  becoming 
dry,  by  wetting  it  with  a  little  water  from  time  to  time. 
The  piece  of  wood  or  cork  upon  which  the  frog  is  laid  is 
often  made  to  give  place  to  the  "frog-plates,"  supplied  by 
opticians.  These  are  made  of  brass,  somewhat  resembling 
the  piece  of  wood  above  recommended,  but  each  maker's 
pattern  differs,  according  to  his  own  taste. 

The  tongue  of  the  frog  is  also  sometimes  used  for  the 
purpose  of  showing  the  circulation  of  the  blood,  which  is 
done  in  the  following  manner  : — The  body  is  wrapped  with 
calico,  and  made  fast  to  the  plate  as  before,  only  the  mouth 
of  the  frog  is  brought  to  the  opening.  The  tongue  is  then 
gently  drawn  out  of  the  month  and  pinned  down  over  the 
aperture,  when  the  circulation  will  be  well  shown.  But,  as 
Dr.  Carpenter  observes,  the  cruelty  of  this  mode  of  treat- 
ment is  so  repulsive  that  it  is  unjustifiable. 

Tadpoles  of  the  frog  (which,  of  course,  are  only  obtainable 
in  their  season)  are  good  subjects  for  showing  the  circula- 
tion of  the  blood.  They  are  best  suited  for  the  microscope 
when  about  one  inch  long.  The  tadpoles  of  the  newt  and 
toad  also  are  equally  suitable.  They  may  be  placed  in  a 
very  shallow  glass  trough  with  a  little  water,  and  a  narrow 
band  of  linen  bound  lightly  round  in  some  part  not  required 
for  examination,  to  keep  them  from  moving ;  or  they  may 
be  laid  upon  a  glass  plate  with  a  drop  or  two  of  water,  and 
a  thin  glass  covering  lightly  bound  upon  it.  Dr.  Carpenter, 
however,  places  them  first  in  cold  water,  gradually  adding 
warm  until  the  whole  becomes  about  100°,  when  the  tadpole 
becomes  rigid,  whilst  the  circulation  is  still  maintained.  I 
have  not,  however,  found  this  necessary,  the  thin  glass  ac- 


198  PREPARATION   AND   MOUNTING 

complishing  all  that  is  desired.  The  tail  is  generally  the 
most  transparent,  and  shows  the  circulation  best ;  bat  in 
some  of  the  newt  larvas  the  blood  may  be  traced  down  to 
the  very  extremities  if  they  are  not  too  old.  Mr.  Whitney 
places  the  tadpole  npon  its  back,  by  which  means  the  heart 
and  other  internal  arrangements  may  be  seen. 

Amongst  fishes  also  may  be  found  subjects  for  the  same 
purpose,  but  they  seldom  furnish  such  good  examples  as 
those  before  mentioned,  because  the  blood-vessels  are  not 
nearly  so  abundant  as  in  the  foot  of  the  frog,  &c.  The 
stickleback  is,  however,  procurable  almost  in  any  place 
during  the  summer  months,  and  may  be  laid  in  a  shallow 
trough,  loosely  bound  down  as  the  tadpole.  The  tail  may 
be  covered  with  a  piece  of  thin  glass  to  prevent  him  curling 
it  to  the  object-glass.  The  power  needed  for  this  will  be 
about  the  same  as  with  the  other  subjects ;  viz.,  a  half  to 
a  quarter-inch  object-glass. 

It  is  not  absolutely  necessary  to  go  to  reptiles  or  fishes 
for  this  curious  sight,  as  some  other  animals  serve  very 
well.  In  the  wings  of  the  common  bat  may  be  found  a 
good  subject.  These  must  be  stretched  out  on  something 
resembling  the  frog-plate  before  .described,  when  those  parts 
near  to  the  bones  will  show  the  largest  vessels  very  clearly. 
The  ear  of  a  young  mouse  is  an  illustration  of  the  same 
phenomenon,  but  it  is  very  difficult  to  fix  it  in  a  good 
position,  as  these  animals  are  so  very  timid  and  restless. 

Amongst  insects  also  the  circulation  may  be  seen  by 
placing  them  in  the  cage,  or  live-box,  so  as  to  keep  them 
still,  but  not  to  injure  them  by  too  much  pressure.  In 
certain  larvae  it  is  particularly  well  shown,  as  in  those  of  the 
day-fly  and  plumed  gnat ;  but  in  some  of  these  the  blood  is 
almost  colourless.  In  the  wings  also  of  many  insects  this 
circulation  is  well  seen,  as  in  those  of  the  common  housefly  ; 
but  as  these  parts  become  dry  in  a  few  days,  the  subject 
should  not  be  more  than  twenty-four  hours  old. 

Somewhat  approximating  to  the  forementioned  pheno- 
menon, is  the  rotation  (or  cyclosis)  of  fluid  in  the  cells,  or, 


OF  MICROSCOPIC   OBJECTS.  199 

as  it  is  usually  termed,  the  circulation  of  the  sap,  of  plants. 
This  is  shown  in  certain  vegetable  growths  as  a  constant 
stream  of  thick  fluid,  wherein  small  globules  are  seen ; 
which  stream  flows  round  the  individual  cells,  or  up  the 
leaf,  turning  at  the  extremity,  and  down  again  by  a  different 
but  parallel  channel.  There  is  little  or  no  difficulty  in 
showing  this  in  many  plants ;  but  some  are,  of  course, 
better  than  others,  and  require  a  different  treatment;  we 
will,  therefore,  notice  a  few  of  these.  PeVhaps  the  best  of 
all  is  the  Vallisneria  spiralis,  which  is  an  aquatic  plant, 
frequently  grown  in,  but  not  really  belonging  to,  this 
country.  As  it  somewhat  resembles  grass,  the  leaf  is  not 
used  in  its  natural  state,  but  a  thin  section  cut  lengthwise 
with  a  razor  or  other  sharp  instrument;  this  section,  how- 
ever, is  much  better  when  the  outer  surface  has  been  first 
removed.  It  should  then  be  laid  upon  a  slide  with  a  drop 
or  two  of  water,  and  covered  with  a  piece  of  thin  glass. 
Often  the  cutting  of  the  section  seems  to  be  such  a  shock  to 
the  leaf  that  no  motion  is  visible  for  awhile,  bat  in  a  short 
time  the  warmth  of  an  ordinary  sitting-room  will  revive  it, 
and  with  a  quarter-inch  object-glass  the  currents  will  be 
rendered  beautifully  distinct.  Where  the  stream  is  un- 
usually obstinate,  the  warmth  may  be  slightly  increased,  but 
too  high  a  heat  destroys  the  movement  altogether.  In  the 
summer,  any  of  the  leaves  show  this  circulation  very 
well ;  but  in  the  winter,  the  slightly  yellow  ones  are  said  to 
be  the  best. 

The  Vallisneria  requires  to  be  cut  in  sections  to  show 
this  circulation ;  but  there  are  many  plants  of  which  it  is 
but  necessary  to  take  a  fragment  and  lay  it  upon  the  slide. 
The  Anacliaris  alsinastrum  is  one  of  these  :  it  grows  in 
water,  having  three  leaves  round  the  stem,  then  a  bare  por- 
tion, again  another  three  leaves,  and  so  on.  One  of  these 
leaves  must  be  plucked  close  to  the  stem,  and  laid  upon  a 
slide  with  a  drop  of  water.  Thin  glass  should  be  placed 
upon  it,  and  along  the  mid-rib  of  the  leaves  the  circulation 
may  be  seen  most  beautifully  when  a  good  specimen  has 


200  PBEPARATION   AND   MOUNTING 

been  chosen ;  but  it  requires  rather  more  power  than  the 
Vallisneria.  This  plant  is  very  common  in  many  parts  of 
the  country,  a  great  number  of  our  ponds  and  streams  being 
literally  choked  up  by  it.  In  the  Chara  vulgaris  and  two  or 
three  of  the  Nitellas,  &c.,  this  phenomenon  may  also  be  seen 
with  no  preparation  except  plucking  a  part  from  the  stem 
and  laying  it  upon  a  slide,  as  with  the  Anacharis.  In  using 
the  Frog-bit,  the  outer  part  of  the  young  leaf-buds  must  be 
taken  to  obtain  the  best  specimens  for  this  purpose ;  but  a 
section  of  the  stem  will  also  show  the  circulation,  though  not 
so  well.  The  plants  before  mentioned  are  all  aquatic,  but 
the  same  movement  of  the  globules  has  been  observed  in 
several  kinds  of  land  plants ;  as  in  the  hairs  upon  the  leaf- 
stalks of  the  common  groundsel ;  but  these  do  not  show  it 
so  well,  nor  are  they  so  easily  managed  as  the  preceding. 

Many  microscopista  who  are  not  fortunate  enough  to  be 
in  the  neighbourhood  of  these  plants  (indeed  the  Vallisneria 
is  a  foreign  one)  grow  them  in  jars  ;  so  a  few  remarks  as  to 
the  treatment  they  require  will  not  be  out  of  place.  The 
Vallisneria  requires  a  temperature  not  lower  than  55°  or 
60°,  and  even  a  higher  degree  than  this  renders  its  growth 
quicker;  and  no  great  change  must  take  place:  the  more 
equable  the  temperature  the  more  healthy  will  the  plant  be. 
A  glass  jar  should  be  taken,  having  an  inch  or  two  of  mould 
at  the  bottom,  which  must  be  pressed  down  closely,  and  the 
plant  must  be  set  in  this.  Water  must  then  be  gently 
poured  in,  so  as  not  to  disturb  the  mould.  As  this  plant 
flourishes  best  when  the  water  is  frequently  changed, 
Mr.  Quekett  recommends  that  the  jar  should  be  occasionally 
placed  under  a  tap  of  water,  and  a  very  gentle  stream 
allowed  to  fall  into  it  for  several  hours,  by  which  means 
much  of  the  confervoid  growth  will  be  removed  and  the 
plant  invigorated.  The  Anacharis  may  be  rooted  in  the 
earth  like  the  Vallisneria,  but  a  small  detached  piece  may  be 
thrown  into  the  jar  of  water  and  there  left  until  wanted. 
For  months  the  circulation  will  be  well  shown  by  it,  and  it  will 
probably  grow  and  increase.  It  is  also  very  healthy  in  an 


OF    MICROSCOPIC    OBJECTS.  201 

in-door  aquarium.  It  is  recommended  that  the  jars  in 
which  the  plants  of  Chara  are  grown  should  be  moved  about 
as  little  as  possible,  as  the  long  roots  are  very  tender,  and 
will  not  bear  agitation. 

An  object  which  is  interesting  to  the  microscopist,  as 
well  as  the  unscientific  observer,  is  the  growth  of  seeds,  as  it 
is  often  erroneously  termed.  A  shaving  of  the  outside  of 
the  seed  is  taken  and  laid  upon  the  glass  slide;  a  thin 
glass  cover  is  then  placed  upon  it,  and  a  drop  of  water 
applied  to  its  edge.  The  water  will  gradually  flow  under 
the  glass  and  reach  the  section  of  the  seed,  when  transparent 
fibres  will  appear  to  spring  out  and  "  grow "  for  some 
minutes.  This,  however,  is  produced  by  the  unfolding  of  a 
spiral  formation  in  the  cells,  and,  therefore,  has  really  no 
similarity  to  the  true  growth.  The  seeds  of  the  Salvias, 
Collomias,  Senecio,  Euellia,  &c.,  are  well  suited  for  the 
display  of  this  curious  sight. 

To  watch  the  development  of  the  spores  of  ferns,  and  the 
fertilization  and  products,  Dr.  Carpenter  recommends  the 
following  mode  of  proceeding: — "Let  a  frond  of  a  fern, 
whose  fructification  is  mature,  be  laid  upon  a  piece  of  fine 
paper,  with  its  spore-bearing  surface  downwards ;  in  the 
course  of  a  day  or  two  this  paper  will  be  found  to  be  covered 
with  a  very  fine  brownish  dust,  which  consists  of  the  dis- 
charged spores.  This  must  be  carefully  collected,  and 
should  be  spread  upon  the  surface  of  a  smoothed  fragment 
of  porous  sandstone ;  the  stone  being  placed  in  a  saucer, 
the  bottom  of  which  is  covered  with  water,  and  a  glass 
tumbler  being  inverted  over  it,  the  requisite  supply  of 
moisture  is  insured,  and  the  spores  will  germinate  luxuriantly. 
Some  of  the  prothallia  soon  advance  beyond  the  rest ;  and 
at  the  time  when  the  advanced  ones  have  long  ceased  to 
produce  antheridia,  and  bear  abundance  of  archegonia,  those 
which  have  remained  behind  in  their  growth  are  beginning 
to  be  covered  with  antheridia.  If  the  crop  be  now  kept 
with  little  moisture  for  several  weeks  and  then  suddenly 
watered,  a  large  number  of  antheridia  and  archegonia 


202  PREPARATION   AND   MOUNTING 

simultaneously  open,  and  in  a  few  hours  afterwards  the 
surface  of  the  larger  prothallia  will  be  found  almost  covered 
with  moving  antherozoids.  Such  prothallia  as  exhibit 
freshly -opened  archegonia  are  now  to  be  held  by  one  lobe 
between  the  forefinger  and  thumb  of  the  left  hand,  so  that 
the  upper  surface  of  the  prothallium  lies  upon  the  thumb ; 
and  the  thinnest  possible  sections  are  then  to  be  made  with 
a  narrow-bladed  knife  perpendicularly  to  the  surface  of  the 
prothallium.  Of  these  sections,  which  after  much  practice 
may  be  made  no  more  than  l-15th  of  a  line  in  thickness, 
some  will  probably  lay  open  the  canals  of  the  archegonia, 
and  within  these,  when  examined  with  a  power  of  200  or 
300  diameters,  antherozoids  may  be  occasionally  distin- 
guished." 

Another  interesting  object  to  the  young  microscopist  is 
afforded  by  the  spores  of  the  Equiseta  (or  Horsetails,  as 
they  are  often  called).  These  may  be  obtained  by  shaking 
the  higher  portion  of  the  stems  when  the  spores  are  ripe. 
They  will  then  fall  like  small  dust,  and  may  be  placed 
under  the  microscope.  The  spores  are  then  seen  to  consist 
of  a  somewhat  heart-shaped  mass  with  bands  rather  in- 
tricately curled  around  it.  As  they  dry,  these  bands 
expand,  and  are  seen  to  be  four  lines  at  right  angles,  with 
the  ends  clubbed,  as  it  may  be  called.  If,  whilst  watching 
them,  the  spores  are  breathed  upon,  these  bands  immediately 
return  to  their  former  state,  and  are  closely  curled  around 
the  spore ;  but  as  they  gradually  dry,  again  expand.  This 
experiment  may  be  repeated  many  times,  and  is  a  very 
interesting  one. 

The  preceding  are  the  principal  objects  which  could  not 
possibly  be  included  in  any  of  the  former  chapters,  but 
would  have  left  a  most  interesting  branch  untouched  had  it 
been  neglected.  There  is  another  subject  also  which  should 
not  be  passed  by;  viz.,  the  production  of  minute  pictures 
which  serve  as  objects  for  microscopic  examination.  I 
may  here  mention  that  as  this  manual  is  simply  to 
enable  the  student  to  prepare  and  mount  his  objects,  the 


OF  MICEOSCOPIC  OBJECTS.  203 

photography  of  magnified  objects  has  evidently  no  place 
here. 

Few  slides  caused  so  ranch  astonishment  as  these  minute 
photographs  when  first  exhibited ;  small  spots  were  seen  to 
contain  large  pictures,  and  a  page  of  printed  matter  was 
compressed  into  the  one-hundredth  part  of  a  square  inch. 
It  would  be  impossible  in  this  place  to  give  the  inquirer 
any  instruction  in  the  manipulation  of  photography,  so  it 
must  be  assumed  that  he  already  knows  this. 

We  will  first  consider  the  process  performed  by  artificial 
light.  The  collodion  employed  in  photographing  generally 
shows  as  much  structure  when  magnified  as  is  found  in 
linen  of  moderate  texture ;  but  this  is  not  always  the  case, 
as  some  samples  bear  much  enlargement  without  any  of 
this  appearance.  It  is  evident  that  a  structure  so  coarse 
would  make  it  entirely  unfit  for  these  minute  pictures,  as 
all  the  small  markings  would  be  destroyed,  or  so  interfered 
with,  that  no  great  enlargement  would  be  practicable.  To 
obtain  almost  structureless  collodion  is  not  an  easy  matter, 
and  a  clever  practitioner  in  this  branch  of  photography 
states  that  he  knows  of  no  method  to  accomplish  this  with 
certainty,  but  he  himself  tries  different  samples  until  he 
falls  upon  a  suitable  one,  which  he  then  lays  aside  for  this 
object.  A  beneficial  effect  is  often  derived  from  keeping  the 
collodion  awhile,  but  this  is  not  always  the  case.  The  slides 
should  be  chosen  of  an  equal  thickness,  so  that  when 
focussed  upon  one,  no  re-adjustment  may  be  necessary  for 
the  others.  The  glass  should,  of  course,  be  free  from  any 
roughness,  scratches,  or  other  imperfections,  and  of  very 
good  quality  and  colour. 

The  microscope  must  be  placed  in  a  horizontal  position, 
and  the  eye-piece  removed,  the  stage  having  a  small  clip 
upon  it  to  keep  the  prepared  plate  in  position.  The  nega- 
tive must  be  supported  at  a  distance  from  that  end  of  the 
microscope  tube  from  which  the  eye-piece  was  withdrawn. 
This  distance  will,  of  course,  vary  according  to  the  relative 
sizes  of  the  negative  and  desired  picture.  With  an  inch 


204  l-fUEPARATION   AKD   MOUNTING 

object-glass,  which  is  of  a  very  convenient  focus,  it  will  vary 
usually  betwixt  one  and  four  feet.  The  negative  must  be 
lighted  by  an  argand  gas-burner  or  camphine-lamp,  and  the 
rajs  rendered  as  parallel  as  possible  by  a  large  plano-convex 
lens  placed  betwixt  the  light  and  the  negative.  It  is  not 
easy  to  arrange  the  apparatus  so  as  to  get  the  light  uni- 
form; but  a  little  practice  will  soon  obviate  this  difficulty. 
Ordinary  ground-glass  is  too  coarsely  grained  to  focus  upon, 
as  the  magnifying  power  used  to  examine  the  minute  reflec- 
tion must  be  considerable.  One  of  the  slides  must  therefore 
be  coated  with  collodion,  submitted  to  the  silver-bath,  and 
after  washing  with  water,  allowed  to  dry.  Upon  this  may 
be  focussed  the  reflected  image,  and  its  minuteness  examined 
with  a  powerful  hand-magnifier,  or  another  microscope 
placed  behind  in  a  horizontal  position.  When  the  utmost 
sharpness  of  definition  is  obtained,  it  is  usually  necessary  to 
remove  the  plate  a  little  distance  from  the  object-glass,  as 
those  for  the  microscope  are  slightly  over-corrected,  so  that 
the  chemical  rays  which  accomplish  the  photography  are 
beyond  the  visual  ones.  The  exact  distance  required  to 
give  a  picture  to  show  the  greatest  distinctness  cannot  be 
given  by  rule;  but  experiments  must  be  made  at  first,  and 
it  will  always  be  the  same  with  the  object-glass  which  we 
have  tested. 

The  plate  may  now  be  prepared  as  in  ordinary  photo- 
graphy, and  placed  upon  the  stage  whilst  the  light  is 
shaded.  When  all  is  ready,  the  shade  is  removed  and  the 
process  allowed  to  go  on,  usually  for  thirty  or  forty  seconds ; 
but  no  certain  rule  can  be  given  as  to  the  required  time,  on 
account  of  the  variety  of  collodions,  lamps,  and  powers  used. 
It  may  be  here  mentioned,  that  it  is  well  to  contrive  some 
little  frame  to  receive  the  prepared  plate,  as  the  silver-bath 
solution  is  liable  to  get  upon  the  microscope-stage,  and  so, 
to  say  the  least,  disfigure  it.  When  the  exposure  has  been 
continued  sufficiently  long,  the  picture  may  be  developed  by 
any  of  the  ordinary  methods,  but  some  of  the  best  produc- 
tions have  been  brought  out  by  the  aid  of  pyrogallic  and 


OF   MICROSCOPIC   OBJECTS.  205 

citric  acid  solution,  with  the  addition  of  a  little  alcohol. 
The  fixing  may  be  effected  by  a  strong  solution  of  hypo- 
sulphite of  soda,  and  the  picture  should  then  be  very  well 
washed  with  pure  water.  When  dry,  the  photograph  must 
be  mounted  with  Canada  balsam,  in  the  same  manner  as 
any  ordinary  object;  but  great  heat  must  not  be  used,  or 
the  picture  may  be  injured. 

When  ordinary  daylight  is  employed  for  this  purpose,  a 
dark  slide  will  be  required  for  the  prepared  plate,  in  the 
same  way  as  for  photographing  landscapes,  &c.  These 
dark  slides  are  generally  made  by  each  individual  to  suit 
his  particular  arrangements  of  negatives ;  but  it  may 
be  here  recommended  that  the  operator  should  always 
focus  in  the  same  slide  which  he  is  about  to  use,  as  so 
small  a  difference  in  distance  lies  betwixt  perfection  and 
failure. 

For  an  ordinary  student,  perhaps  the  preceding  method  is 
that  which  is  the  most  readily  used,  and  consequently  the 
most  generally  available ;  but  almost  every  one  has  a  dif- 
ferent arrangement  of  microscope,  by  which  he  procures 
these  minute  pictures.  Mr.  Shadbolt  (one  of  our  most 
successful  photographers)  gives  the  following  instructions: — 
"  Having  removed  the  upper  stage-plate  of  a  large  com- 
pound microscope,  I  replace  it  with  one  of  wood,  supplied 
with  guide-pins  of  silver  wire,  in  order  to  admit  of  its  sup- 
porting a  slip  of  glass  coated  with  collodion,  and  excited  in 
the  nitrate  of  silver  bath  in  the  usual  way.  If  the  ordi- 
nary brass  stage-plate  were  left  undisturbed,  it  is  obvious 
that  it  and  the  excited  slip  of  glass  would  be  mutually 
destructive. 

"  The  microscope  is  now  to  be  placed  in  a  horizontal 
position,  the  objective,  intended  to  produce  the  picture, 
made  to  occupy  the  place  usually  filled  by  the  achromatic 
condenser  on  the  sub-stage  of  the  microscope,  while  another 
objective  is  screwed  into  the  lower  end  of  the  body  of  the 
instrument,  which  is  used  not  only  to  focus  with,  but_also 
to  make  the  requisite  allowance  for  actinic  variation. 


206  PREPARATION   AND   MOUNTING 

"  The  negative  intended  to  be  reduced  is  then  arranged 
vertically,  with  its  centre  in  the  axis  of  the  microscopic 
body,  at  a  distance  from  two  to  four  feet  from  the  lower 
object-glass,  and  with  a  convenient  screen  of  card,  wood,  or 
thick  paper,  to  cut  off  any  extraneous  light  that  would 
otherwise  pass  beyond  the  limits  of  the  picture. 

"  A  small  camphine-lamp  is  employed  for  the  purpose  of 
illuminating  the  negative,  having  a  good  bull's-eye  lens  as 
a  condenser,  so  arranged  with  its  flat  side  next  the  lamp 
that  the  refracted  rays  shall  just  fill  the  whole  of  a  double 
convex  lens  of  about  six  inches  in  diameter,  the  latter  being 
placed  in  such  a  position  as  to  refract  the  rays  of  light  in  a 
parallel  direction  upon  the  negative.  By  this  arrangement 
the  bull's-eye  lens  of  about  two  inches  and  a  half  in 
diameter  appears  as  the  source  of  the  light  instead  of  the 
small  flame  of  the  lamp. 

"  By  using  a  bat's-wing  gas-burner  of  a  good  size,  a  single 
lens,  instead  of  the  two,  may  be  so  placed  as  to  give  the 
necessary  uniformity  of  illumination." 

This  arrangement  requires  the  same  care  in  working  as 
that  before  mentioned,  the  pictures  being  produced,  de- 
veloped, and  fixed  by  the  same  treatment. 

It  is  certain  that  almost  every  manipulator  makes  some 
small  changes  in  the  method  of  producing  these  minute  pic- 
tures ;  but  the  rules  given,  though  far  from  new,  are 
sufficient  for  all  purposes ;  and  I  may  say  with  truth,  that 
those  which  I  procured  when  these  wonders  were  quite  new, 
are  fully  equal  in  every  respect  to  the  best  usually  met  with 
at  the  present  time. 

With  these  instructions  I  shall  close  my  Handbook,  as  I 
believe  that  nearly  every  branch  of  the  Preparation  and 
Mounting  of  Microscopic  Objects  has  been  treated  of.  Not 
that  the  beginner  can  expect  that  he  has  only  to  read  this 
to  be  able  to  mount  everything;  but  that  there  are  difficul- 
ties from  which  he  may  be  freed  by  instruction,  when  other- 
wise he  would  have  been  compelled  to  learn  by  failure  alone. 
I  may  here,  however,  repeat  certain  advice  before  given, — 


OF  MICEOSCOPIC   OBJECTS.  207 

that,  when  practicable,  it  is  a  good  thing  to  mount  each 
object  by  two  or  more  different  methods,  as  very  frequently 
one  feature  is  best  shown  dry,  another  in  liquid,  and  a  third 
in  balsam.  Secondly,  let  no  failures  discourage  you  in 
following  up  what  will  assuredly  one  day  become  a  source  of 
great  pleasure,  and  render  your  daily  constitutional  walk, 
which  is  often  dull  in  the  extreme,  very  delightful,  as  it  will 
afford  you  some  new  wonder  in  every  hedge-row.  And, 
lastly,  let  the  mounting  be  studied  thoroughly,  scarcely  any 
part  of  microscopie  science  being  more  worthy  of  thought 
than  this,  since  it  will  so  far  contribute  to  the  enjoyment 
or  instruction  of  others,  as  to  preserve  for  their  examination, 
objects  which  have  already  ministered  to  your  own,  but 
which  may  yet  be  so  perishable  as  to  be  speedily  lost  unless 
some  one  of  the  many  processes  described  in  this  manual  be 
employed  for  their  preservation. 


INDEX. 


209 


INDEX. 


A. 

PAGE 

ACARDDA     110 

Acid,  acetic   5 

Acid,  carbolic   127 

Acid,  chlorhyd 5 

Acid,  hippuric  114 

Acid,  hydrofluoric    19 

Acid,  hyperosmie     9 

Acid,  nitric 5,  61,  62 

Acid,   nitric,   with    chlorate 

of  potash    6 

Acid,  oxalic   6 

Acid,  phosphoric 5 

Acid,  sulphuric   6,  11 

Acid,  tannic  5 

Agents,  "differentiating"...       5 

Agents,  hardening  9 

Agents,   softening    13 

Agents,  staining 7 

Air-bubbles    42 

Air-bubbles,  to  expel 91 

Albumin 16 

Alcohol    5,  6,  9,  17 

Algte  and  desmids,  to  pre- 
serve     127 

Algse,  to  preserve    125 

Ammonia  5 

Ammonia,  molybdate  of 7 

Ammonia,  oxalurate  of  112 

Ammonias,  liquor 14,  67 

Anatomical  specimens,  Bru- 
netti's  mode  of  preparing  164 

Aniline  colours 7 

Animal  tissues,  dissection  of  163 

Anise,  oil  of  7 

Antennae 107,  137 

Antennae,  to  bleach 107 

Asphaltum 45,  49 


B. 

PACK 

BALSAM  and  Chloroform 44 

Balsam,  Canada   7 

Baryta  water    6 

Bath  for  injections  177 

Bath,  hot-water,  cheap    93 

Beaker  glasses  65 

Benzole 17,  19 

Benzole— Benzine    75 

Berg-mehl 72 

Blights   87 

Blood-discs    83 

Blood-stains,  to  detect   84 

Blue,  Prussian  8 

Boiling   11 

Bone,  chips  of,  stained  149 

Bone,  sections  of 148 

Bones,  fossil,  sections  of    ...  150 

Bones,  softened    15 

Bottle-washing 76 

Brain  and  spinal  cord,  sec- 
tions of  166 

Breeding-cage    for  podurae, 
Mclntyre's 83 


C. 

CALCAREOUS    matter,     sol- 
vents of 18 

Camphor    20 

Camphor- water 13,  123 

Canada  balsam 43 

Canada  balsam  and  benzole    90 

Carmine  solution 7 

Casein     16 

Cassia,  oil  of 7 

Castor  oil 19,127 


210 


INDEX. 


Castor  oil,  to  mount  crystals 


113 


Cells,  built  up  129 

Cells,  brass    31 

Cells,  of  card 29 

Cells,  epithelial    7 

Cells,  how  to  fill  with  balsam    95 

Cells  for  test  objects   32 

Cells,  ivory    31 

Cells,  leather    30 

Cells,  paper  56 

Cells,  pill-box    31 

Cells,  Piper's < 

Cells,  tin,  zinc  31 

Cells  to  fill 132 

Cells,  wooden    29 

Cellulose  in  coal  144 

Cement  cells   54,  128 

Cement,  Dr.  Bastian's    129 

Cement,  electrical   46 

Cement,  Marion   47 

Cements 43 

Cerebral  tissue 13 

Chalk,  organisms  in 98 

Chamber,  moist    22 

ChonHrin    17 

Chromic  acid 9 

Circulation  in  Anacharis  and 

Vallisneria 199 

Circulation  in  foot  and  tongue 

of  frog,  to  see   196 

Circulation  in  insects 198 

Circulation  in  tadpoles    197 

Clips,  spring 41 

Cloves,  oil  of 7 

Coal,  cannel  144 

Coal  sections 143 

Colours  for  inj  ections 178 

Condenser,  cheap    51 

Coniferous  wood  144 

Corallines  81 

Coral  sections    143 

Comea,  nerves  of 159 

Covers,  glass,  to  cut    26 

Covers,  ornamental  paper  ...     57 

Covers,  glass,  to  clean    28 

Covers,  to  gauge    27,  28 

Creosote 7 

Crystallization  Ill 


PAGE 

Crystallization,  compound...  115 

Crystals,  sections  of    157 

Cuticles,  siliceous     121 


D. 

DAMMAR 44 

Dammar  and  benzole  20 

Dammar  cement  45 

Deane's  compound  125 

Decalcifying  process  141 

Diamond  beetle  88 

Diatomaceas  58,  60 

Diatomaceae,  cleansing  of  ...  61 
Diatomacese,  collection  of  ...  59 
Diatoms,  cleansing  of  by  Mr. 

Rylands 63 

Diatoms  in  situ,  to  mount  by 

Rylands' method  136 

Diatoms,  to  bleach 65 

Diatoms,  to  mount 63,  67,  69 

Diatoms,  to  mount  in  Canada 

balsam  97 

Differentiation,  chemical  ...  5 
Differentiation,  mechanical  5,  7 

Digester,  Papin's 15 

Disc  revolver,  Beck's  53 

Dissection 160 

Drying  11 

Drying  tissues,  Mr.  Suffolk's 

process  159 

Dyticus,  foot  of  109 

Dyticus,  spiracles  of  109 

Dyticus,  wings  of  109 


E. 

EARTH,  Bermuda 72 

Echini,  spines  of  142 

Eggs  of  insects,  to  preserve  137 

Equiseta,  spores  of 202 

Equisetum,  cuticle  of 120 

Electricity 21 

Elutriation 66 

Entomostraca    ..  ..134 


INDEX. 


211 


PACK 

Ether 19 

Eye-pieces,  deep 4 

Eyes  of  insects 106 


F. 

FABRANTS,  Mr.,  his  medium  124 

Feathers  of  birds 110 

Feet  of  insects 108 

Ferns,  fructification  of    201 

Ferns,  scales  of. 84 

Ferns,  spores  of  85 

Fibrin 16 

File  or   Rubber,    corundum  140 

Filter,  tube    77 

Finishing   58 

Fish,  scales  of  88 

Fish,  tails  and  fins  of 84 

Flint,  sections  of 146 

Flustra  avicularis 119 

Foraminifera 73 

Foraminifera,  sections  of  ...     78 
Foraminifera,  to  cleanse...  74,  75 

Forceps  37 

Forceps,  bulldog 176 

Forceps,  compressing 38,  39 

Forceps,  Goode's 39 

Forceps,  Page's    38 

Forceps,  Spencer's  41 

Forceps,  wooden 38 

Freezing  tissues   11 

Froar,  cornea  of 8 

Fruit-stones,  sections  of 150 

Fuchsine    

Fungi  and  moulds   87 


G. 

GELATINE 17, 177 

Geranium,  petal  of 80 

Gills  of  fish    168 

Gizzards 173 

Glass-engraving    19 

Glue    177 

Glue,  liquid  46 

Glue,  marine 45 

Glycerine...  5,  7, 10,  13,  124,  137 


PACK 

Glycerine  and  gum 124 

Glycerine  jelly 125 

Glycerine,  refractive  powei 

of 14 

Glycerine,  use  of,  by  Messrs. 

Suffolk  and  Hislop  138 

Goadby,  Mr 186 

Goadby's  fluid  126 

Goadby 's  solution     164 

Gold,  chloride  of  8,  159 

Gold,   chloride   of,  and  po- 
tassium        8 

Guano,  diatoms  in   70 

Guano,  diatoms  in,  by  Mr. 

Roberts  71 

Guano,  spurious  72 

Gum    7 

Gum-water    47 

Gum-water,   extra  adhesive    47 


H. 

H.EMATOXYLINE    7 

Hairs  89 

Hairs,  sections  of. 152 

Hardening  tissue 9 

Heat,  use  of 14 

Horn  178 

Horn,  sections  of 150 

Horny  matters  softened 14 

Horse-hair,    plaited  for  po- 

lariscope 118 

Hyperosmic  acid 10 


I. 


INDIGO    7 

Infusoria,  fossil 72 

Injection,   blue,  transparent  187 

Injection,  carmine   188 

Injection,  machine  for    182 

Injection,  process  of    180 

Injections  175 

Injections  by  double  decom- 
position    179 

Injections,  Dale's  method  ... 
Injections,    Doyer's  method  185 


212 


PACK 

Injections,  to  mount  184 

Injections,  transparent  186 

Injections,  twofold 184 

Injections,  various  189 

Insects,  bleaching  of  21 

Insects,  examination   of,  by 

polarized  light 21 

Insects,  eyes  of 10,  89 

Insects,  internal  organs  of...     17 

Insects,  legs  and  feet  of 88 

Insects,  muscles  of 21 

Insects,  scales  of 81 

Insects,  to  mount  in  balsam  104 

Insects,  tracheae  of 92 

Inversion  of  objects 50 

Iodine....  5 


J. 


JAPAN  black 


46 


K. 


KERATIN    17 

Kesteven  on  brain  and  spinal 

cord 12 

Kidney,  injected  166 

Knives,  dissecting  .........37,  161 


L. 

LABELLING  on  glass    19 

Labels 49 

Laminae,  thin    15 

Lamp,  Bunsen's   42 

Lamp,  spirit 42 

Larvae,  skins  of 84 

Lathe  for  sections,  Butter- 
worth's    144 


Leaves 
Leaves 
Leaves 


cuticle  of 79 

hairy 79,  86 


parenchyma  of 


17 


Leaves  sections  of  154 

Lenses   immersion  23 

Lieberkiihn    89 

Light,  polarized    20 


PACK 

Lime-water    6 

Liver,  injected 166 

Lung,  injected 166 


M. 

MACERATION    13, 15,  162 

Mayflies 138 

Mercury  bichloride 9,  11 

Mercury  nitrate  17 

Metal   capsules   for   Canada 

balsam    94 

Microscope,  dissecting   160 

Microscope,  Gairdner's  64 

Microscope,  inverted  22 

Mosses  and  Algae 133 

Mosses,  fructification  of 85 

Mosses,  to  preserve 125 

Mounting,  dry 52 

Mounting  in  Canada  balsam    90 

Mouth  of  insects 109 

Muscle    164 

Muscular  fibre  ...  15 


N. 

NAILS,  softened    15 

Needles,  curved    176 

Needles,  dissecting 161 

Needles,  use  of 37 

Nerve-tissue 13,  165 

Neutral  media 2 

Neutral  tints 20 

Nitric  acid 80 

Nummulites 17 


0. 

OATMEAL,  parched  11 

Objectives  of  wide  angle    ...  4 

Objects   small,  to  take  up...  36 

Oils,  essential   19 

Oily  and  fatty  matters   19 

Oily  and  fatty  matters,  sol- 
vents of 19 

Onion,  raphides  of  120 


INDEX. 


213 


PAGE 

Osmic  acid 8 

Ossein 15,  17 

Oysters,  young 117 

P. 

PALATES  of  molluscs  169 

PaleaB  of  cereals   121 

Palladium,  chloride  of 10 

Palladium,  proto- chloride  of      8 

Paraffine  12,  158 

Pencils,  camel-hair 36 

Photography,  microscopic...  203 

Picric  acid 7,  8 

Pipette  66 

Podura,  scales  of 82 

Polariscope,    to    mount  ob- 
jects for Ill 

Pollens    80 

Polycystinse  99 

Polycystinse,  to  cleanse 100 

Polyzoa  135 

Porcupine,  quill  of  151 

Potash,  bichromate  of  9,  10 

Potash,  chlorate  of 5 

Potassse,  liquor    5,  13,  14 

Potassium,  ferro-cyanide    ...       8 

Potassium,  iodide  of   8 

Preservative  liquids 123 

Pump,  air  42 

R. 

RAPHIDES 86 

Raphides  for  polariscope    ...  120 

Retina 13 

Rings,  glass 130 

Rings,  iron 131 

Rings,  vulcanite   131 

Rings,  zinc  and  tin 131 

Rods,  glass,  pointed    37 

Rods  of  cochlea  of  ear 10 

Rush,  sections  of 154 


S. 

SALTCINE    113 

Santonine  113 


Saw,  watch-spring   140 

Scales  of  eel  117 

Scales  of  fish 117 

Scales  of  plants 121 

Scissors,  dissecting   37,  161 

Sea-mats    87 

Sea  soundings  75 

Section-cutter  153 

Sections 139 

Seeds  81 

Seeds  and  pollen  110 

Seeds,  growth  of 201 

Seeds,  sections  of. 158 

Sertularidae    119 

Shells,  pearly,  section  of   ...  142 

Shells,  sections  of    140 

Silica,  colloid    18 

Silica,  or  silicic  acid    18 

Silica,  vegetable  67 

Siliceous  matter,  solvents  of  18 

Silver,  nitrate  of 8 

Size,  gold  45 

Skin     17 

Skin,  sections  of  158 

Slides,  concave 130 

Slides,  glass  24 

Slides,  gauge  for  25 

Slides,  to  clean 25,  94 

Slides,   to   cover  and  orna- 
ment      57 

Soda,  caustic 9 

Sodse,  liquor 5,  13,  14 

Soda,  tartrate  of 114 

Soft  tissues,  sections  of 155 

Softening  tissues 13 

Spicer,   the    Rev.    W.   W.'s 

preservative  fluid 127 

Spicula  of  sponges   103 

Spider,  poison-glands  of 168 

Spinal  cord    165 

Spiracles    168 

Spleen,  injected   166 

Sponge,  sections  of 156 

Stage  of  microscope,  hot   ...  22 

Staining 7 

Staining,  double  7 

Staining  nerves    159 

Stand,  Mr.  Loy's 51 

Stand,  universal  50 


214 


INDEX. 


PAGE 

Starches 119 

Star-fish 78 

Stomach  of  molluscs    170 

Sublimate,  corrosive    17 

Sugar 7 

Syringe  175 

Syringe  for  balsam  93 

Syriuge,  glass    162 

Syrup 14 


T. 

TABLE,  brass 42 

Tannic  acid,  or  Tannin  6 

Tannin  9,  11,  17 

Teasing  by  needles 3 

Teeth,  sections  of  92,  146 

Teeth,  softened     15 

Tendon  17 

Testae 18 

Thwaites  liquid    126 

Tin  tubes,  collapsible 44 

Tongues  of  molluscs    169 

Tongues  or  palates  of  mol- 

lusca    118 

Tracheae  of  insects  109,  167 

Trongh,  dissecting  162 

Tubes,  dipping 37 

Turntable,  Mr.  Hislop's 33 

Turntable,  Dr.  Matthews'...     34 
Turntable,  Mr.  Shadbolt's...     33 


PACK 

Turpentine  7,  19 

Turpentine,  spurious  91 


V. 

VALENTIN'S  knife 155,  184 

Varnish,  black 48 

Varnish,  caoutchouc  48 

Varnish,  sealing-wax  48 

Vegetable  tissues,  dissection 
of....  ..  162 


W. 

WATCH-GLASSES  41 

Water-bath    22 

Wine-glasses,  broken 42 

Whalebone    14 

Whalebone,  sections  of  151 

Wood,  fossil  144 

Wood,  sections  of 152 


Z. 

ZINC,  chloride  of 126 

Zoophytes 87 

Zoophytes,  to  mount  103 

Zoophytes,   to  preserve,  by 
Dr.  Bird's  method    ..        ..101 


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